Low density composite proppant, filtration media, gravel packing media, and sports field media, and methods for making and using same

ABSTRACT

Low density composite particles made of a binder and filler material are provided for use in subterranean formations. The filler includes low density filler and optionally other filler. The binder includes a polymer and optionally cement. The particles may be employed as proppants useful to prop open subterranean formation fractures. The particles are also useful for gravel packing in subterranean formations, water filtration and artificial turf for sports fields. Methods of making the composite particles are also disclosed.

[0001] The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/450,588, filed Nov. 30, 1999, which is acontinuation-in-part of Patent Cooperation Treaty application No.PCT/US99/16507, filed Jul. 22, 1999, which claims priority from U.S.provisional patent application No. 60/093,672, filed Jul. 22, 1998, allof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to low density composite media tobe used in filtration and composite proppant to be used in petroleum andgas production to “support/prop” a hydraulic fracture in the vicinity ofa wellbore. The proppant keeps the hydraulic fracture open for theinflow of petroleum and/or natural gas, and can substantially improvethe yield per well. More particularly, the invention relates to aparticle suitable as composite proppants, composite filtration media andcomposite media for cushioning artificial turf for a sports field. Theparticles are built from suitable fillers bonded together with organicand/or inorganic tri-dimensional crosslinkers/binders. The inventionalso relates to methods for making and using these filtration media,proppants and cushioning media.

[0004] 2. Description of Background Art

[0005] In general, proppants are extremely useful to keep open fracturesimposed by hydraulic fracturing upon a subterranean formation, e.g., anoil or gas bearing strata. Typically, the fracturing is desired in thesubterranean formation to increase oil or gas production. Fracturing iscaused by injecting a viscous fracturing fluid or a foam at highpressure into the well to form fractures. As the fracture is formed, aparticulate material, referred to as a “propping agent” or “proppant” isplaced in the formation to maintain the fracture in a propped conditionwhen the injection pressure is released. As the fracture forms, theproppants are carried into the well by suspending them in additionalfluid or foam to fill the fracture with a slurry of proppant in thefluid or foam. Upon release of the pressure, the proppants form a packwhich serves to hold open the fractures. The goal of using proppants isto increase production of oil and/or gas by providing a highlyconductive channel in the formation. Choosing a proppant is critical tothe success of well stimulation.

[0006] The propped fracture thus provides a highly conductive channel inthe formation. The degree of stimulation afforded by the hydraulicfracture treatment is largely dependent upon formation parameters, thefracture's permeability and the fracture's propped width. If theproppant is an uncoated substrate, e.g., sand, and is subjected to highstresses existing in a gas/oil well, the substrate may be crushed toproduce fines of crushed proppant. Fines will subsequently reduceconductivity within the proppant pack. However, a resin coating willenhance crush resistance of a coated particle above that of thesubstrate alone.

[0007] Glass beads had been used as propping materials (see U.S. Pat.No. 4,068,718, incorporated herein by reference for the state of thetechnology). Their disadvantages include the costs of energy andproduction, as before, and their severe drop in permeability at elevatedpressures (above about 35 MPa) because of their excessive crushing atdownhole conditions. Thus, it is not currently favored.

[0008] Three different types of propping materials, i.e., proppants, arecurrently employed.

[0009] The first type of proppant is a sintered ceramicgranulation/particle, usually aluminum oxide, silica, or bauxite, oftenwith clay-like binders or with incorporated hard substances such assilicon carbide (e.g., U.S. Pat. No. 4,977,116 to Rumpf et al,incorporated herein by reference, EP Patents 0 087 852, 0 102 761, or 0207 668). The ceramic particles have the disadvantage that the sinteringmust be done at high temperatures, resulting in high energy costs. Inaddition, expensive raw materials are used. They have relatively highbulk density, and often have properties similar to those of corundumgrinding materials, which cause high wear in the pumps and lines used tointroduce them into the drill hole.

[0010] The second type of proppant is made up of a large group of knownpropping materials from natural, relatively coarse, sands, the particlesof which are roughly spherical, such that they can allow significantflow (English “frac sand”) (see U.S. Pat. No. 5,188,175 for the state ofthe technology).

[0011] The third type of proppant includes samples of type one and twothat may be coated with a layer of synthetic resin (U.S. Pat. No.5,420,174 to Deprawshad et al; U.S. Pat. No. 5,218,038 to Johnson et aland U.S. Pat. No. 5,639,806 to Johnson et al (the disclosures of U.S.Pat. Nos. 5,420,174, 5,218,038 and 5,639,806, incorporated herein byreference); EP Patent No. 0 542 397).

[0012] Known resins used in resin coated proppants include epoxy, furan,phenolic resins and combinations of these resins. The resins are fromabout 1 to about 8 percent by weight of the total coated particle. Theparticulate substrate for resin coated proppants may be sand, ceramics,or other particulate substrate and typically has a particle size in therange of USA Standard Testing screen numbers from about 8 to about 100(i.e. screen openings of about 0.0937 inch to about 0.0059 inch).

[0013] Resin coated proppants come in two types: precured and curable.Precured resin coated proppants comprise a substrate coated with a resinwhich has been significantly crosslinked. The resin coating of theprecured proppants provides crush resistance to the substrate. Since theresin coating is already cured before it is introduced into the well,even under high pressure and temperature conditions, the proppant doesnot agglomerate. Such precured resin coated proppants are typically heldin the well by the stress surrounding them. In some hydraulic fracturingcircumstances, the precured proppants in the well would flow back fromthe fracture, especially during clean up or production in oil and gaswells. Some of the proppant can be transported out of the fracturedzones and into the well bore by fluids produced from the well. Thistransportation is known as flow back.

[0014] Flowing back of proppant from the fracture is undesirable and hasbeen controlled to an extent in some instances by the use of a proppantcoated with a curable resin which will consolidate and cure underground.Phenolic resin coated proppants have been commercially available forsome time and used for this purpose. Thus, resin-coated curableproppants may be employed to “cap” the fractures to prevent such flowback. The resin coating of the curable proppants is not significantlycrosslinked or cured before injection into the oil or gas well. Rather,the coating is designed to crosslink under the stress and temperatureconditions existing in the well formation. This causes the proppantparticles to bond together forming a 3-dimensional matrix and preventingproppant flow back.

[0015] These curable phenolic resin coated proppants work best inenvironments where temperatures are sufficiently high to consolidate andcure the phenolic resins. However, conditions of geological formationsvary greatly. In some gas/oil wells, high temperature (>180° F.) andhigh pressure (>6,000 psi) are present downhole. Under these conditions,most curable proppants can be effectively cured. Moreover, proppantsused in these wells need to be thermally and physically stable, i.e., donot crush appreciably at these temperatures and pressures.

[0016] Curable resins include (i) resins which are cured entirely in thesubterranean formation and (ii) resins which are partially cured priorto injection into the subterranean formation with the remainder ofcuring occurring in the subterranean formation.

[0017] Many shallow wells often have downhole temperatures less than130° F., or even less than 100° F. Conventional curable proppants willnot cure properly at these temperatures. Sometimes, an activator can beused to facilitate curing at low temperatures. Another method is tocatalyze proppant curing at low temperatures using an acid catalyst inan overflush technique. Systems of this type of curable proppant havebeen disclosed in U.S. Pat. No. 4,785,884 to Armbruster and thedisclosure of this patent is incorporated by reference in its entirety.In the overflush method, after the curable proppant is placed in thefracture, an acidic catalyst system is pumped through the proppant packand initiates the curing even at temperatures as low as about 70° F.This causes the bonding of proppant particles.

[0018] Due to the diverse variations in geological characteristics ofdifferent oil and gas wells, no single proppant possesses all propertieswhich can satisfy all operating requirements under various conditions.The choice of whether to use a precured or curable proppant or both is amatter of experience and knowledge as would be known to one skilled inthe art.

[0019] In use, the proppant is suspended in the fracturing fluid. Thus,interactions of the proppant and the fluid will greatly affect thestability of the fluid in which the proppant is suspended. The fluidneeds to remain viscous and capable of carrying the proppant to thefracture and depositing the proppant at the proper locations for use.However, if the fluid prematurely loses its capacity to carry, theproppant may be deposited at inappropriate locations in the fracture orthe well bore. This may require extensive well bore cleanup and removalof the mispositioned proppant.

[0020] It is also important that the fluid breaks (undergoes a reductionin viscosity) at the appropriate time after the proper placement of theproppant. After the proppant is placed in the fracture, the fluid shallbecome less viscous due to the action of breakers (viscosity reducingagents) present in the fluid. This permits the loose and curableproppant particles to come together, allowing intimate contact of theparticles to result in a solid proppant pack after curing. Failure tohave such contact will give a much weaker proppant pack.

[0021] Foam, rather than viscous fluid, may be employed to carry theproppant to the fracture and deposit the proppant at the properlocations for use. The foam is a stable foam that can suspend theproppant until it is placed into the fracture, at which time the foambreaks. Agents other than foam or viscous fluid may be employed to carryproppant into a fracture where appropriate.

[0022] Also, resin coated particulate material, e.g., sands, may be usedin a wellbore for “sand control.” In this use, a cylindrical structureis filled with the proppants, e.g., resin coated particulate material,and inserted into the wellbore to act as a filter or screen to controlor eliminate backwards flow of sand, other proppants, or subterraneanformation particles. Typically, the cylindrical structure is an annularstructure having inner and outer walls made of mesh. The screen openingsize of the mesh being sufficient to contain the resin coatedparticulate material within the cylindrical structure and let fluids inthe formation pass therethrough.

[0023] While useful proppants are known, it would be beneficial toprovide proppants having improved features such as good flow back, goodcompressive strength, as well as good long term conductivity, i.e.,permeability, at the high closure stresses present in the subterraneanformation. Flow back, as discussed above, relates to keeping theproppant in the subterranean formation. Compressive strength relates topermitting the proppant to withstand the forces within the subterraneanformation. High conductivity directly impacts the future production rateof the well. It would be especially beneficial to provide such proppantsfrom raw materials which can be obtained and processed at relatively lowand moderate cost, as well as a process for producing them, such thatthe formed particle will produce less wear in the equipment used tointroduce it into the drill hole because of its low bulk density and itssmooth surface.

[0024] A separate area of proposed use is in water filtration. In manyindustrial and non industrial situations there is a need to be able toextract solids from a stream of water. There is a wide range offiltration systems designed to meet these requirements. Most of thesesystems use a solid particulate to form a filtration pack through whichthe water containing the solid flows. The particulate (filtration media)retains the solid within the pore space of the pack and allows the waterto pass through (with a lower solids content). Periodically, the filtermust be back flushed to remove the trapped solids so that the filtrationprocess can continue. A filtration media should have the followingtraits:

[0025] a high particle surface area so that there are many opportunitiesto trap the solids.

[0026] the lowest possible density so that the number of pounds requiredto fill the filter and the flow rate required to back flush (a processthat expands the volume of the filter pack) are both minimized.

[0027] be acid/base/solvent resistant so that the media's integrity isunaffected by the presence of these materials.

[0028] be non toxic in nature so that undesirable chemicals are notleached into the water stream being filtered.

[0029] have the ability to be made in various sizes (20/40, 16/30, etc.)and densities so that filter packs can be designed to extract a varietyof particles.

[0030] Examples of currently used filtration media are sand, ceramics,activated charcoal and walnut hulls.

OBJECTS OF THE INVENTION

[0031] It is an object of the present invention to provide low densityproppants comprising filler, selected from at least one member of thegroup consisting of finely divided minerals, fibers, walnut shells,almond shells, and coconut shells, bound by binder.

[0032] It is another object of the present invention to provide lowdensity filtration media for extracting solids from a water streamcomprising filler, selected from at least one member of the groupconsisting of finely divided minerals, fibers, walnut shells, almondshells, and coconut shells, bound by binder and/or cement.

[0033] It is another object of the present invention to provide methodsof using proppant, or filtration media, comprising filler, selected fromat least one member of the group consisting of finely divided minerals,fibers, walnut shells, almond shells, and coconut shells, bound bybinder and/or cement.

[0034] It is another object of the present invention to provide methodsof using gravel packing media, comprising filler, selected from at leastone member of the group consisting of finely divided minerals, fibers,walnut shells, almond shells, and coconut shells, bound by binder and/orcement.

[0035] It is another object of the present invention to provideparticles for use on artificial turf sports fields.

[0036] These and other objects of the present invention will becomeapparent from the following specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The following briefly describes the drawing of the presentspecification, wherein like elements are identified by like numbers.

[0038]FIG. 1 shows a process flow diagram of a first embodiment of aprocess for making particles of the present invention.

[0039]FIG. 2 shows a process flow diagram of a second embodiment of aprocess for making particles of the present invention.

[0040]FIG. 3 shows a process flow diagram of a third embodiment of aprocess for making particles of the present invention.

[0041]FIG. 4 shows a process flow diagram of the process of FIG. 3modified to include recycle of particles.

[0042]FIG. 5 shows a first embodiment of a particle of proppant orfiltration media of the present invention.

[0043]FIG. 6 shows a second embodiment of a particle of proppant orfiltration media of the present invention.

[0044]FIG. 7 shows a process flow diagram of a cold set process formaking cores and coating cores with polyurethane.

[0045]FIG. 8 shows a process flow diagram of a cold set process formaking cores and coating cores with an epoxy resin.

[0046]FIG. 9 shows a process flow diagram of a cold set process formaking cores and coating cores with a furan resin of formaldehyde andfurfuryl alcohol.

[0047]FIG. 10 shows a process flow diagram of a cold set process formaking proppant particles of filler and ALPHASET binder and ALPHASETcoating.

[0048]FIG. 11 shows a simplified process flow diagram of a firstembodiment of a process for making proppants or filtration media of thepresent invention with melamine/phenol-formaldehyde as a binder and as acoating.

[0049]FIG. 12 shows a process for making proppant of the presentinvention from cement/phenol-formaldehyde polymer compositions.

[0050]FIG. 13 shows a process for making proppant of the presentinvention from macro defect free (MDF) cement.

[0051]FIG. 14 shows a first embodiment of a sports field employing theparticles of the present invention.

[0052]FIG. 15 shows a second embodiment of a portion of a sports fieldemploying the particles of the present invention.

SUMMARY OF THE INVENTION

[0053] The invention provides a composite particle for proppant orfiltration media comprising filler particles, e.g., finely dividedmineral or finely divided mineral and fiber, bound by a suitable organicor inorganic binder. A typical organic binder is selected from at leastone member of the group consisting of a phenolic resole resin orphenolic novolac resin, urethanes (for example polyol resins, e.g.,phenolic resin, dissolved in petroleum solvents which are cross-linkablewith a polymeric isocyanate using an amine catalyst, such as SIGMA SETresins available from Borden Inc., Louisville, Ky.), alkaline modifiedresoles set by esters (for example, ALPHASET resins available fromBorden Inc., Louisville, Ky.), melamine, and furans. Typical inorganicbinders include silicates, e.g., sodium silicate, phosphates, e.g.,polyphosphate glass, borates, or mixtures thereof, e.g., silicate andphosphate. Typical binders for the present invention also may beselected from polymer/cement combinations and MDF cement.

[0054] The filler particles may be any of various kinds of commerciallyavailable filler, selected from at least one member of the groupconsisting of finely divided minerals, fibers, ground almond shells,ground walnut shells, and ground coconut shells.

[0055] The finely divided minerals include at least one member of thegroup consisting of fly ash, silica (quartz sand), alumina, mica,silicate, e.g., orthosilicates or metasilicates, calcium silicate,kaolin, talc, zirconia, boron and glass, e.g., glass microspheres.

[0056] The fibers include at least one member selected from the groupconsisting of milled glass fibers, milled ceramic fibers, milled carbonfibers and synthetic fibers, having a softening point above about 200°F. so as to not degrade, soften or agglomerate during production or use.

[0057] The amount and material of the one or more filler materials, aswell as the resin and optional cement, are selected such that thecomposite particle has a bulk density of 0.50 to 1.30 grams per cubiccentimeter (gm/cm³), preferably 0.95 to 1.10 gm/cm³, and a grain density(particle density) of 0.90 to 2.20 gm/cm³, preferably 1.40 to 1.60gm/cm³. For example, a composite particle may comprise a low densityfiller material (such as ground walnut shells) together with a higherdensity filler material (such as finely divided silica), and a binder ofpolymer resin and cement, so long as the respective amounts of theseingredients results in a composite particle having the desired lowdensity. Low density is advantageous in many uses because it facilitatestransporting the composite particles and facilitates injection into thesubterranean formation. For example, low density gravel packing is veryadvantageous because it is easy to use.

[0058] The present composite particles are substantially spherical. Thecomposite particles typically have a sphericity of at least 0.7,preferably at least 0.85, and most preferably at least 0.90, as measuredaccording to API Method RP56 Section 5.

[0059] The composite particles are made by mixing filler particlesselected from at least one member of the group consisting of finelydivided minerals, fibers, ground walnut shells, ground almond shells,and ground coconut shells with at least one binder. A typical silicatefiller is NEPHELINE SYENITE, a whole grain sodium potassium aluminasilicate available from Unimin Corporation, New Canaan, Conn. Inparticular, the composite particles are made by mixing the fillerparticles with a first portion of binder to form substantiallyhomogeneous core particles of granulated product comprising the fillerparticles and the first portion of binder. By “substantiallyhomogeneous” it is meant that the core particle has an absence of alarge substrate particle as common, for example, for coated sandproppants. To strengthen the composite particles, a second portion ofbinder may be coated onto the core particles of granulated product. Thecore binders are preferably precured. The outer coating resins arecurable or precured.

[0060] For purposes of this application, the term “cured” and“crosslinked” are used interchangeably for the hardening which occurs inan organic binder. However, the term “cured” also has a broader meaningin that it generally encompasses the hardening of any binder, organic orinorganic, to form a stable material. For example, crosslinking, ionicbonding and/or removal of solvent to form a bonded material in its finalhardened form may be considered curing. Thus, mere removal of solventfrom an organic binder prior to crosslinking may or may not be curingdepending upon whether the dry organic binder is in final hardened form.

[0061] Optionally, the uncoated composite particles or coated proppantparticles are dried, but not cured (e.g., crosslinked), and then undergoa mechanical refining of the surface to smooth it to make it asubstantially spherical shape. However, drying may lead to undesiredagglomeration. Thus, the benefits and detriments of drying should beconsidered when deciding whether to include a drying step.

[0062] The composite particles, as described in this invention havespecial and unique properties such as controlled plasticity andelasticity behavior. Because of these unique properties, the compositeparticles can be applied as the sole proppant in a 100% proppant pack(in the hydraulic fracture) or as a part replacement of existingcommercial available ceramic and/or sand-based proppants, resin-coatedand/or uncoated, or as blends between those. The composite particles canalso be employed as the sole media in a 100% filtration pack or blendedwith other filtration media.

[0063] As applied, the composite particles used as proppants improveflow-back control of the pack, and decrease the forming and generationof fines when used to fill 100% of the fracture or used in a combinationpack with other commercially available proppants. As applied, thecomposite particles also greatly reduce the detrimental effects ofembedment and subsequent fines generation (that are the result of theembedment process) that is commonly associated with the use of othercommercially available proppants. The reduction in embedment can beattributed to the elastic nature of the composite and its ability tobetter distribute the downhole stresses. Combining all of theseproperties of the composite particle will lead to increase in theconductivity/permeability of the pack.

[0064] Selecting the below-specified volume proportions of filler andsynthetic binder give surprisingly good flexural resistance strength,which is also a measure of a steelball-pointed strength and hardness(Brinell Strength). This is a very important factor for the use of thepresent materials as proppants. The flexural strengths are generallysomewhat higher when quartz sand is used as the mineral than withaluminum oxide.

[0065] The proppant according to the invention has higher resistance tocompressive forces than some ceramic proppants, and therefore has lessgrain failure. This reduces point stresses and generates less fines(which can damage fracture conductivity) than previous experience wouldlead one to expect just from the absolute values of the breakingstrength. The preferred sphericity φ is greater than 0.9, specificallydue to the use of appropriate post-processing measures.

[0066] The invention also provides improved methods of using theabove-described particles as media for water filtration, gravel packing,or as curable and/or precured proppants for treating subterraneanformations.

[0067] The invention also provides improved artificial turf sportsfields and methods of using the above-described particles as media forartificial turf sports fields.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] The filler particles of the present invention may be employedwith any conventional proppant resin. The type of resin and fillermaking up the proppant will depend upon a number of factors includingthe probable closure stress, formation temperature, and the type offormation fluid.

[0069] The term resin includes a broad class of high polymeric syntheticsubstances. Resin includes thermosetting materials, thermoplasticmaterials, and cold setting materials.

[0070] Specific thermosets include epoxy which is a heat set resin whenused with a phenolic, (however, epoxy sets with formaldehyde at varioustemperatures), phenolic, e.g., resole (a true thermosetting resin) ornovolac (thermoplastic resin which is rendered thermosetting by ahardening agent), polyester resin, epoxy-modified novolac, furan, andmelamine resin.

[0071] Epoxy-modified novolac is disclosed by U.S. Pat. No. 4,923,714 toGibb et al incorporated herein by reference. The phenolic resincomprises any of a phenolic novolac polymer; a phenolic resole polymer;a combination of a phenolic novolac polymer and a phenolic resolepolymer; a cured combination of phenolic/furan resin or a furan resin toform a precured resin (as disclosed by U.S. Pat. No. 4,694,905 toArmbruster incorporated herein by reference); or a curablefuran/phenolic resin system curable in the presence of a strong acid toform a curable resin (as disclosed by U.S. Pat. No. 4,785,884 toArmbruster). The phenolics of the above-mentioned novolac or resolepolymers may be phenol moieties or bis-phenol moieties. Resole resinsare preferred.

[0072] Another heat set binder is polymer/cement combinations in whichthe polymer comprises a phenol-aldehyde polymer, polyamide, polyimide orolefins such as polyethylene or straight or branched chainpolypropylene.

[0073] Specific thermoplastics include polyethylene,acrylonitrile-butadiene styrene, polystyrene, polyvinyl chloride,fluoroplastics, polysulfide, polypropylene, styrene acrylonitrile,nylon, and phenylene oxide. Another typical resin is latex.

[0074] Among the synthetic rubber polymer bases useful for the purposesof the invention, unsaturated chain polymers or copolymers obtained bypolymerization of conjugated dienes and/or aliphatic or aromatic vinylmonomers are preferred.

[0075] More particularly, the polymer bases may be selected from thegroup comprising: natural rubber, 1,4-cis polybutadiene,polychloroprene, 1,4-cis polyisoprene, optionally halogenatedisoprene-isobutene copolymers, butadiene-acrylonitrile,styrene-butadiene and styrene-butadiene-isoprene terpolymers, eitherprepared in solution or in emulsion, ethylene-propylene-dieneterpolymers.

[0076] Specific cold setting resins include epoxy resins cured with anamine when used alone or with polyurethane, polyurethanes, alkalinemodified resoles set by esters (ALPHASETs), furans, e.g., furfurylalcohol-formaldehyde, urea-formaldehyde, and free methylol-containingmelamines set with acid. For the purposes of this description, a coldset resin is any resin which can normally be cured at room temperature.Typically cold set resins cure at a temperature less than 150° F. Thus,for example, at 200° F., phenol-formaldehyde resin heat cures.

[0077] Urethanes are disclosed by U.S. Pat. No. 5,733,952 to Geoffrey.Melamine resins are disclosed by U.S. Pat. Nos. 5,952,440, 5,916,966,and 5,296,584 to Walisser. ALPHASET resins are disclosed by U.S. Pat.Nos. 4,426,467 and Re. 32,812 (which is a reissue of U.S. Pat. No.4,474,904) all of which are incorporated herein by reference.

[0078] Macrodefect free (MDF) cement is disclosed by U.S. Pat. Nos.5,814,146; 5,147,459; 4,353,746; 4,353,747; 4,353,748; 4,410,366;4,070,199 and the publication Macro-defect-free Cement: A Review, Mat.Res. Soc. Symp. 179 (1991), pp. 101-121, all of which are incorporatedherein by reference. MDF cements employ high alumina cement and watersoluble polymer such as poly vinyl alcohol or polyacrylamide. MDFcements can also employ high alumina cement and a water resistantpolymer such as urethane according to European patent application No.0280971 to Kataoka et al, incorporated herein by reference. Europeanpatent application No. 0021628, incorporated herein by reference,discloses a high alumina MDF cement product modified by the addition ofpolyvinyl alcohol/acetate.

[0079] Polymer resin cement comprises high alumina cement, anhydrousresin precursor, organic solution agent and additives. Polymer resincement is disclosed by the publication Hasegawa, M., et al, A New Classof High Strength, Water and Heat Resistant Polymer-Cement CompositeSolidified By an Essentially Anhydrous Phenol Resin Precursor, Cementand Concrete Research 25 (1995) 6, pp. 1191-1198, U.S. Pat. Nos.5,651,816 to Kobayashi et al, 4,003,873 to Smith, 5,785,751 to Bashlykovet al, 4,820,766 to Lahalih et al, and 5,478,391 to Babaev et al, all ofwhich are incorporated herein by reference.

[0080] A. Filler Particles

[0081] The filler particles should be inert to components in thesubterranean formation, e.g., well treatment fluids, and be able towithstand the conditions, e.g., temperature and pressure, in the well.Filler particles, e.g., one or more of ground almond shells, groundcoconut shells, ground walnut shells, finely divided minerals andfibers, of different dimensions and/or materials may be employedtogether. The finely divided mineral filler particle is typicallymonocrystalline in nature, to be more abrasion resistant, and thusenhance the ability of the composite particle to withstand pneumaticconveying.

[0082] It is important that the dimensions and amount of fillerparticles, as well as the type and amount of resin, be selected so thatthe filler particles remain within the resin of the proppant rather thanbeing loosely mixed with proppant particles. The containment of fillerparticles prevents loose particles from clogging parts, e.g., screens,of an oil or gas well. Moreover, the attachment prevents loose particlesfrom decreasing permeability in the oil or gas well.

[0083] It is also important that the amount and material of the one ormore filler materials, as well as the resin and optional cement, areselected such that the composite particle has a bulk density of 0.50 to1.30 grams per cubic centimeter (gm/cm³), preferably 0.95 to 1.10gm/cm³, and a grain density (particle density) of 0.90 to 2.20 gm/cm³,preferably 1.40 to 1.60 gm/cm³. For example, a composite particle maycomprise a low density filler material (such as ground walnut shells)together with a higher density filler material (such as finely dividedsilica) bound by polymer resin and cement, so long as the respectiveamounts of these ingredients results in a composite particle having thedesired light density.

[0084] 1. Finely Divided Minerals

[0085] The finely divided minerals include at least one member of thegroup consisting of silica (quartz sand), alumina, fumed carbon, carbonblack, graphite, mica, silicate, calcium silicate, calcined oruncalcined kaolin, talc, zirconia, boron and glass. Microcrystallinesilica is especially preferred. A typical silicate for use as filler isNEPHELINE SYENITE, a whole grain sodium potassium alumina silicateavailable from Unimin Corporation, New Canaan, Conn.

[0086] The particles of finely divided minerals range in size from about2 to about 60 μm. Typically, the particles of minerals have a d₅₀ ofabout 4 to about 45 μm, preferably about 4 to about 6 μm. The parameterd₅₀ is defined as the diameter for which 50% of the weight of particleshave the specified particle diameter. Preferred filler would be angularor subangular rather than rounded in shape. One example of suchpreferred material is MIKRODORSILIT 120L microcrystalline silica flour,available from Capital Gebr. Dorfner GmbH and Company, Germany.

[0087] Most mineral fillers have a grain density of 2.45 to 3.20 gr/cm³,preferably 2.50 to 2.80 gr/cm³. However, some potential mineral fillersinclude those which make the proppant particle less dense, such as flyash or hollow glass microspheres. Hollow glass microspheres have a graindensity of 0.57 to 0.82 gr/cm³, preferably 0.60 to 0.65 gr/cm³.

[0088] Fly ash, with a typical SiO₂ content between 40 and 60% by weightand typical Al₂O₃ content between 20 and 40% by weight, can also be usedas the mineral to save materials costs for certain requirements. Fly ashhas a grain density of 1.10 to 1.50 gr/cm³, preferably 1.15 to 1.20gr/cm³. The typical grain size of this material (d₅₀) is up to 35 μm, sothat grinding down to the preferred value of 4 to 6 μm might still beconducted. The fly ash should have a minimal amount of carbon, whosepresence would weaken the proppant particle.

[0089] 2. Fibers

[0090] The fibers may be any of various kinds of commercially availableshort fibers. Such fibers include at least one member selected from thegroup consisting of milled glass fibers, milled ceramic fibers, milledcarbon fibers, natural fibers, and synthetic fibers, e.g., crosslinkednovolac fibers, having a softening point above typical startingtemperature for blending with resin, e.g., at least about 200° F., so asto not degrade, soften or agglomerate.

[0091] The typical glasses for fibers include E-glass, S-glass, andAR-glass. E-glass is a commercially available grade of glass fiberstypically employed in electrical uses. S-glass is used for its strength.AR-glass is used for its alkali resistance. The carbon fibers are ofgraphitized carbon. The ceramic fibers are typically alumina, porcelain,or other vitreous material.

[0092] Fiber lengths range from about 6 microns to about 3200 microns(about ⅛ inch). Preferred fiber lengths range from about 10 microns toabout 1600 microns. More preferred fiber lengths range from about 10microns to about 800 microns. A typical fiber length range is about0.001 to about {fraction (1/16)} inch. Preferably, the fibers areshorter than the greatest length of the substrate. Suitable,commercially available fibers include milled glass fiber having lengthsof 0.1 to about {fraction (1/32)} inch; milled ceramic fibers 25 micronslong; milled carbon fibers 250 to 350 microns long, and KEVLAR aramidfibers 12 microns long. Fiber diameter (or, for fibers of non-circularcross-section, a hypothetical dimension equal to the diameter of ahypothetical circle having an area equal to the cross-sectional area ofthe fiber) range from about 1 to about 20 microns. Length to aspectratio (length to diameter ratio) may range from about 5 to about 175.The fiber may have a round, oval, square, rectangular or otherappropriate cross-section. One source of the fibers of rectangularcross-section may be chopped sheet material. Such chopped sheet materialwould have a length and a rectangular cross-section. The rectangularcross-section has a pair of shorter sides and a pair of relativelylonger sides. The ratio of lengths of the shorter side to the longerside is typically about 1:2-10. The fibers may be straight, crimped,curled or combinations thereof.

[0093] 3. Ground Shells

[0094] As stated above, a typical low density filler materials are oneor more materials selected from the group consisting of ground almondshells, ground coconut shells and ground walnut shells. These shells areground to finely divided particles which range in size from about 2 toabout 60 μm. Typically, the particles have a d₅₀ of about 4 to about 45μm, preferably about 4 to about 6 μm. It is theorized that because theseground shells are porous, they absorb resin to strengthen the compositeparticle.

[0095] Ground almond shells have a grain density of 1.30 to 1.50 gr/cm³,preferably 1.35 to 1.45 gr/cm³. Ground coconut shells have a graindensity of 1.30 to 1.50 gr/cm³, preferably 1.35 to 1.45 gr/cm³. Groundwalnut shells have a grain density of 1.30 to 1.50 gr/cm³, preferably1.35 to 1.45 gr/cm³.

[0096] B. Phenolic Resole and/or Novolac Resins

[0097] 1. Resole Resins

[0098] The phenol-aldehyde resole resin has a phenol:aldehyde molarratio from about 1:1 to about 1:3, typically from about 1:1 to about1:1.95. A preferred mode of preparing the resole resin is to combinephenol with a source of aldehyde such as formaldehyde, acetaldehyde,propionaldehyde, furfural, benzaldehyde or paraformaldehyde underalkaline catalysis. During such reaction, the aldehyde is present inmolar excess. It is preferred that the resole resin have a molar ratioof phenol to formaldehyde from about 1:1.1 to 1:1.6. The resoles may beconventional resoles or modified resoles. Modified resoles are disclosedby U.S. Pat. No. 5,218,038, incorporated herein by reference in itsentirety. Such modified resoles are prepared by reacting aldehyde with ablend of unsubstituted phenol and at least one phenolic materialselected from the group consisting of arylphenol, alkylphenol,alkoxyphenol, and aryloxyphenol.

[0099] Modified resole resins include alkoxy modified resole resins. Ofalkoxy modified resole resins, methoxy modified resole resins arepreferred. However, the phenolic resole resin which is most preferred isthe modified orthobenzylic ether-containing resole resin prepared by thereaction of a phenol and an aldehyde in the presence of an aliphatichydroxy compound containing two or more hydroxy groups per molecule. Inone preferred modification of the process, the reaction is also carriedout in the presence of a monohydric alcohol.

[0100] Phenols suitable for preparing the modified orthobenzylicether-containing phenolic resole resins are generally any of the phenolswhich may be utilized in the formation of phenolic resins, and includesubstituted phenols as well as unsubstituted phenol per se. The natureof the substituent can vary widely, and exemplary substituted phenolsinclude alkyl-substituted phenols, aryl-substituted phenols,cycloakyl-substituted phenols, alkenyl-substituted phenols,alkoxy-substituted phenols, aryloxy-substituted phenols andhalogen-substituted phenols. Specific suitable exemplary phenols includein addition to phenol per se, o-cresol, m-cresol, p-cresol, 3,5-xylenol,3,4-xylenol, 3,4,5-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol,p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol,p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotylphenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol,p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol. Apreferred phenolic compound is phenol itself.

[0101] The aldehyde employed in the formation of the modified phenolicresole resins can also vary widely. Suitable aldehydes include any ofthe aldehydes previously employed in the formation of phenolic resins,such as formaldehyde, acetaldehyde, propionaldehyde and benzaldehyde. Ingeneral, the aldehydes employed contain from 1 to 8 carbon atoms. Themost preferred aldehyde is an aqueous solution of formaldehyde.

[0102] Metal ion catalysts useful in production of the modified phenolicresins include salts of the divalent ions of Mn, Zn, Cd, Mg, Co, Ni, Fe,Pb, Ca and Ba. Tetra alkoxy titanium compounds of the formula Ti(OR)₄where R is an alkyl group containing from 3 to 8 carbon atoms, are alsouseful catalysts for this reaction. A preferred catalyst is zincacetate. These catalysts give phenolic resole resins wherein thepreponderance of the bridges joining the phenolic nuclei areortho-benzylic ether bridges of the general formula —CH₂(OCH₂)_(n)—where n is a small positive integer.

[0103] A molar excess of aldehyde per mole of phenol is used to make themodified resole resins. Preferably the molar ratio of phenol to aldehydeis in the range of from about 1:1.1 to about 1:2.2. The phenol andaldehyde are reacted in the presence of the divalent metal ion catalystat pH below about 7. A convenient way to carry out the reaction is byheating the mixture under reflux conditions. Reflux, however, is notrequired.

[0104] To the reaction mixture is added an aliphatic hydroxy compoundwhich contains two or more hydroxy groups per molecule. The hydroxycompound is added at a molar ratio of hydroxy compound to phenol of fromabout 0.001:1 to about 0.03:1. This hydroxy compound may be added to thephenol and aldehyde reaction mixture at any time when from 0% (i.e., atthe start of the reaction) to when about 85% of the aldehyde hasreacted. It is preferred to add the hydroxy compound to the reactionmixture when from about 50% to about 80% of the aldehyde has reacted.

[0105] Useful hydroxy compounds which contain two or more hydroxy groupsper molecule are those having a hydroxyl number of from about 200 toabout 1850. The hydroxyl number is determined by the standard aceticanhydride method and is expressed in terms of mg KOH/g of hydroxycompound. Suitable hydroxy compounds include ethylene glycol, propyleneglycol, 1,3-propanediol, diethylene glycol, triethylene glycol,glycerol, sorbitol and polyether polyols having hydroxyl numbers greaterthan about 200. Glycerol is a particularly suitable hydroxy compound.

[0106] After the aliphatic hydroxy compound containing two or morehydroxy groups per molecule is added to the reaction mixture, heating iscontinued until from about 80% to about 98% of the aldehyde has reacted.Although the reaction can be carried out under reflux until about 98% ofthe aldehyde has reacted, prolonged heating is required and it ispreferred to continue the heating only until about 80% to 90% of thealdehyde has reacted. At this point, the reaction mixture is heatedunder vacuum at a pressure of about 50 mm of Hg until the freeformaldehyde in the mixture is less than about 1%. Preferably, thereaction is carried out at 95° C. until the free formaldehyde is lessthan about 0.1% by weight of the mixture. The catalyst may beprecipitated from the reaction mixture before the vacuum heating step ifdesired. Citric acid may be used for this purpose. The modified phenolicresole may be “capped” to be an alkoxy modified phenolic resole resin.In capping, a hydroxy group is converted to an alkoxy group byconventional methods that would be apparent to one skilled in the artgiven the teachings of the present disclosure.

[0107] Metal ion catalysts useful in production of the modified phenolicresole resins include salts of the divalent ions of Mn, Zn, Cd, Mg, Co,Ni, Fe, Pb, Ca and Ba. Tetra alkoxy titanium compounds of the formulaTi(OR)₄ where R is an alkyl group containing from 3 to 8 carbon atoms,are also useful catalysts for this reaction. A preferred catalyst iszinc acetate. These catalysts give phenolic resole resins wherein thepreponderance of the bridges joining the phenolic nuclei areortho-benzylic ether bridges of the general formula —CH₂(OCH₂)_(n)—where n is a small positive integer.

[0108] 2. Phenol-Aldehyde Novolac Polymer-Containing Resins

[0109] An embodiment of the present invention employs resin whichincludes phenol-aldehyde novolac polymer. The novolac may be any novolacemployed with proppants. The novolac may be obtained by the reaction ofa phenolic compound and an aldehyde in a strongly acidic pH region.Suitable acid catalysts include the strong mineral acids such assulfuric acid, phosphoric acid and hydrochloric acid as well as organicacid catalysts such as oxalic acid, or para toluenesulfonic acid. Analternative way to make novolacs is to react a phenol and an aldehyde inthe presence of divalent inorganic salts such as zinc acetate, zincborate, manganese salts, cobalt salts, etc. The selection of catalystmay be important for directing the production of novolacs which havevarious ratios of ortho or para substitution by aldehyde on the phenolicring, e.g., zinc acetate favors ortho substitution. Novolacs enriched inortho substitution, i.e., high-ortho novolacs, may be preferred becauseof greater reactivity in further cross-linking for polymer development.High ortho novolacs are discussed by Knop and Pilato, Phenolic Resins,p. 50-51 (1985) (Springer-Verlag) incorporated herein by reference.High-ortho novolacs are defined as novolacs wherein at least 60% of thetotal of the resin ortho substitution and para substitution is orthosubstitution, preferably at least about 70% of this total substitutionis ortho substitution.

[0110] The novolac polymer typically comprises phenol and aldehyde in amolar ratio from about 1:0.85 to about 1:0.4. Any suitable aldehyde maybe used for this purpose. The aldehyde may be formalin,paraformaldehyde, formaldehyde, acetaldehyde, furfural, benzaldehyde orother aldehyde sources. Formaldehyde itself is preferred.

[0111] The novolacs used in this invention are generally solids such asin the form of a flake, powder, etc. The molecular weight of the novolacwill vary from about 500 to 10,000, preferably 1,000 to 5,000 dependingon their intended use. The molecular weight of the novolacs in thisdescription of the present invention are on a weight average molecularweight basis. High-ortho novolac resins are especially preferred.

[0112] The resin composition typically comprises at least 10 weightpercent novolac polymer, preferably at least about 20 weight percentnovolac polymer, most preferably about 50 to about 70 weight percentnovolac polymer. The remainder of the resin composition could includecrosslinking agents, modifiers or other appropriate ingredients.

[0113] The phenolic moiety of the novolac polymer is selected fromphenols of Formula I or bisphenols of Formula II, respectively:

[0114] R and R¹ are independently alkyl, aryl, arylalkyl or H. InFormula II, R and R¹ are preferably meta to the respective hydroxy groupon the respective aromatic ring. Unless otherwise defined, alkyl isdefined as having 1 to 6 carbon atoms, and aryl is defined as having 6carbon atoms in its ring. In Formula II, X is a direct bond, sulfonyl,alkylidene unsubstituted or substituted with halogen, cycloalkylidene,or halogenated cycloalkylidene. Alkylidene is a divalent organic radicalof Formula III:

[0115] When X is alkylidene, R² and R³ are selected independently fromH, alky, aryl, arylalkyl, halogenated alkyl, halogenated aryl andhalogenated arylalkyl. When X is halogenated alkylidene, one or more ofthe hydrogen atoms of the alkylidene moiety of Formula II are replacedby a halogen atom. Preferably the halogen is fluorine or chlorine. Also,halogenated cycloalkylidene is preferably substituted by fluorine orchlorine on the cycloalkylidene moiety.

[0116] A typical phenol of Formula I is phenol, per se.

[0117] Typical bisphenols of Formula II include Bisphenol A, BisphenolC, Bisphenol E, Bisphenol F, Bisphenol S, or Bisphenol Z.

[0118] The present invention includes novolac polymers which contain anyone of the phenols of Formula I, bisphenols of Formula II, orcombinations of one or more of the phenols of Formula I and/or one ormore of the bisphenols of Formula II. The novolac polymer may optionallybe further modified by the addition of VINSOL®, epoxy resins, bisphenol,waxes, or other known resin additives. One mode of preparing analkylphenol-modified phenol novolac polymer is to combine an alkylphenoland phenol at a molar ratio above 0.05:1. This combination is reactedwith a source of formaldehyde under acidic catalysis, or divalent metalcatalysis (e.g., Zn, Mn). During this reaction, the combination ofalkylphenol and phenol is present in molar excess relative to theformaldehyde present. Under acidic conditions, the polymerization of themethylolated phenols is a faster reaction than the initial methylolationfrom the formaldehyde. Consequently, a polymer structure is built upconsisting of phenolic and alkylphenolic nuclei, linked together bymethylene bridges, and with essentially no free methylol groups. In thecase of metal ion catalysis, the polymerization will lead to methyloland benzylic ethers, which subsequently break down to methylene bridges,and the final product is essentially free of methylol groups.

[0119] 3. Crosslinking Agents and Other Additives for Use with PhenolicNovolacs

[0120] For practical purposes, phenolic novolacs do not harden uponheating, but remain soluble and fusible unless a hardener (crosslinkingagent) is present. Thus, in curing a novolac resin, a crosslinking agentis used to overcome the deficiency of alkylene-bridging groups toconvert the resin to an insoluble infusible condition.

[0121] Appropriate crosslinking agents include hexamethylenetetramine(HEXA), paraformaldehyde, oxazolidines, melamine resin or other aldehydedonors and/or the above-described resole polymers. Each of thesecrosslinkers can be used by itself or in combinations with othercrosslinkers. The resole polymer may contain substituted orunsubstituted phenol.

[0122] A resin composition of this invention typically comprises up toabout 25 weight percent HEXA and/or up to about 90 weight percent resolepolymers based on the total weight of coating composition. Where HEXA isthe sole crosslinking agent, the HEXA comprises from about 5 to about 25weight percent of the resin. Where the phenol-aldehyde resole polymer isthe sole crosslinking agent, the resin contains from about 20 to about90 weight percent of the resole polymer. The composition may alsocomprise combinations of these crosslinkers.

[0123] Additives are used for special cases for special requirements.The resin systems of the invention may include a wide variety ofadditive materials. The resin may also include one or more otheradditives such as a coupling agent such as a silane to promote adhesionof the coating to substrate, a silicone lubricant, a wetting agent, asurfactant, dyes, flow modifiers (such as flow control agents and flowenhancers), and/or anti-static agents. The surfactants may be anionic,nonionic, cationic, amphoteric or mixtures thereof. Certain surfactantsalso operate as flow control agents. Other additives include humidityresistant additives or hot strength additives. Of course, the additivesmay be added in combination or singly.

[0124] 4. Method to Make Resoles

[0125] A typical way to make resoles is to put a phenol in a reactor,add an alkaline catalyst, such as sodium hydroxide or calcium hydroxide,and aldehyde, such as a 50 weight % solution of formaldehyde, and reactthe ingredients under elevated temperature until the desired viscosityor free formaldehyde is achieved. Water content is adjusted bydistillation. Elasticizers or plastizers, such as bisphenol A or cashewnut oil, may also be present to enhance the binder elasticity orplasticity. Other known additives may also be present.

[0126] 5. Method to Make Novolac Polymer

[0127] To make phenolic novolac polymers with one or more phenols ofFormula I, the phenol is mixed with acidic catalyst and heated. Then analdehyde, such as a 50 weight % solution of formaldehyde is added to thehot phenol and catalyst at elevated temperature. Water made by thereaction is removed by distillation to result in molten novolac. Themolten novolac is then cooled and flaked.

[0128] To make novolac polymers with bisphenols of Formula II, thebisphenol is mixed with a solvent, such as n-butyl acetate, at elevatedtemperature. An acid catalyst such as oxalic acid or methane sulfonicacid is then added and mixed with the bisphenol and then an aldehyde,typically formaldehyde, is added. The reactants are then refluxed. It isnoted that the preparation of the novolac resin can occur under acidiccatalysis, or divalent metal catalysis (e.g., Zn, Mn), wherein thebisphenol is present in greater than equimolar amount relative to thesource of aldehyde. After reflux, water is collected by azeotropicdistillation with n-butyl acetate. After removal of the water andn-butyl acetate, the resin is flaked to yield resin products.Alternatively, the polymers can be made using water as a solvent.

[0129] 6. Reacting Aldehyde with Phenol-Aldehyde Novolacs orBisphenol-Aldehyde Novolacs

[0130] Phenol-aldehyde novolacs or bisphenol-aldehyde novolacs may bemodified by reacting these novolacs with an additional quantity ofaldehyde using a basic catalyst. Typical catalysts used are sodiumhydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide (orlime), ammonium hydroxide and amines.

[0131] In the case of phenol-aldehyde polymers or bisphenol-aldehydepolymers, the molar ratio of added aldehyde to phenolic moiety, based onthe phenolic moiety monomeric units in the novolac, ranges from 0.4:1 to3:1, preferably from 0.8:1 to 2:1. This achieves a cross-linkable(reactive) polymer having different chemical structures and generallyhigher molecular weights than the resole polymers obtained by a singlestep process which involves initially mixing bisphenol monomers andaldehyde with an alkaline catalyst at the same molar ratio of thecombined aldehyde and bisphenol. Furthermore, it is feasible to usedifferent aldehydes at different stages of the polymer preparation.

[0132] These polymers can be used alone or with other polymers, such asphenol-aldehyde novolacs, bisphenol-aldehyde novolac, or combinationsthereof, as a crosslinking agent, or as a component of crosslinkingagents. When the aldehyde-modified polymers are employed as crosslinkingagents, they may be used with other typical crosslinking agents such asthose described above for novolac polymers.

[0133] 7. Methods to Make Proppant, Gravel Packing or Filtration Mediawith Resole or Novolac Heat Set Resins

[0134] After making the resole or novolac resins, the crosslinkingagent, resin and filler particles are mixed at conditions to provideeither a precured or curable resin composition, as desired. Whether aresin composition is of the precured or curable type depends upon anumber of parameters. Such parameters include the ratio of the novolacresin to the curing agent; the acidity of the novolac resin; the pH ofthe resole resin; the amount of the crosslinking agent; the time ofmixing the resin compositions and filler particles; the temperature ofthe resin compositions and filler particles during mixing; catalysts (ifany) used during the mixing and other process parameters as known tothose skilled in the art. Typically, the precured or curable proppantsmay contain resole resin in the presence or absence of novolac resin.

[0135]FIG. 1 shows a simplified process flow diagram of a firstembodiment of a process for making proppants, gravel packing, orfiltration media of the present invention. In the process, a binderstream 12 and a filler particle stream 14 are fed to a high intensitymixer 9 to prepare a homogeneous slurry stream 5. Slurry stream 5 feedsa granulator 10 to produce a granulated product stream 16. The binderstream 12 contains resin, water and conventional additives. Typically,the resin is a resole and may act as its own crosslinking agent.Coupling agents are also typical additives. A typical granulator 10 isan Eirich mixer, such as an Eirich R11 mixer, manufactured by EirichMachines, Inc., Gurnee, Ill.

[0136] Typically, the granulator 10 is operated as a batch process andis operated as disclosed generally in EP 308 257 and U.S. Pat. No. Re.34,371, both of which are incorporated herein by reference. For example,EP 308 257 discloses making ceramic particles in an Eirich machinedescribed in U.S. Pat. No. 3,690,622. The machine comprises a rotatablecylindrical container, the central axis of which is at an angle to thehorizontal, one or more deflector plates, and at least one rotatableimpacting impeller usually located below the apex of the path ofrotation of the cylindrical container. The rotatable impacting impellerengages the material being mixed and may rotate at a higher angularvelocity than the rotatable cylindrical container.

[0137] The following sequence occurs in the mixer pelletizer (granulator10): (1) nucleation or seeding at which time slurry is added near theimpacting impeller; (2) growth of the spheroids during which theimpacting impeller rotates at slower speed than during the nucleationstep; and (3) polishing or smoothing the surfaces of the spheroids byturning off the impacting impeller and allowing the cylindricalcontainer to rotate.

[0138] The amount of binder (resin) generally comprises about 10 toabout 30, preferably about 10 to about 25, weight percent of the totaldry materials (resin, filler, etc.) fed to the granulator 10. The amountof binder being a water free value defined as the amount of resin, e.g.,novolac and/or resole, and additives other than water. Typically, themixing occurs in the presence of a coupling agent such as gamma/aminopropel trimethoxy silane. The coupling agent may be added to the mixer 9before, or premixed with the binder stream 12. Typically, 0 to 50% ofthe total binder stream 12 is water. Typically, mixing time ranges from1 to 5 minutes at a pan rotation speed of 50 to 80 rpm and a chopperspeed of 1400 to 1600 rpm. The granulation (nucleation time) ranges fromabout 2 to about 10 minutes with a vessel speed of 25 to 45 rpm and achopper speed of 1400 to 1600 rpm. The smoothing is also known as“chopping.” The temperature of the granulator 10 during the above stepsranges from 10 to 40° C.

[0139] The granulated material stream 16 then passes to a curingapparatus 50. Typically, curing apparatus 50 is a drying oven operatingat a residence time for the granulated material of about 1 minute toabout 2 hours, at a temperature of about 90° to about 200° C.,preferably about 150° to about 190° C. This produces a cured granulatedproduct stream 52 which feeds a screening apparatus 80 to recover aproppant product stream 82 of predetermined product size. A typicalscreening apparatus 80 is a sieve such as a vibrating screen. A typicaldesired proppant particle has a d₅₀ from 0.4 to 0.8 mm, or a particlediameter range of 20 to 40 USS mesh (0.425 to 0.85 mm) or 30 to 40 USSmesh.

[0140]FIG. 2 shows a second embodiment of a process for makingproppants, gravel packing, or filtration media of the present invention.This embodiment resembles the process of FIG. 1 except that thegranulated material stream 16 is fed dried but uncured to a refiningapparatus 15 to mechanically increase the sphericity of the granulatedmaterial to a sphericity of at least about 0.8, preferably at leastabout 0.85, and more preferably at least about 0.9, and produce a stream17 of such mechanically treated material.

[0141] This step performs a mechanical refining of the surface to makeit approximately a spherical shape. For example, this is typically doneeither by putting the granules of FIG. 2, dried at 40° C., but notcured, in a granulating pan with a high tilt angle and high rotationalspeed, or by processing them in a SPHERONIZER device, manufactured byCalvera Process Solutions Limited, Dorset, England, at 400-1000 rpm forabout 3 to about 30 minutes. The smoothing occurred by a removal process(grinding process) in which the particles in a profiled rotating pan arethrown out against a cylindrical wall and then rolled back onto theplate of the pan.

[0142] Alternatively, the particles may be smoothed and compressed byrolling before curing.

[0143]FIG. 3 shows a process flow diagram of a third embodiment of aprocess for making proppants or gravel packing of the present invention.

[0144] The process is similar to that of FIG. 2 except that the curedgranulated product stream 52 is fed to a coating apparatus 60 whichcoats/impregnates the cured granulated material of stream 52 withadditional resin from a second binder stream 61. This produces proppantparticles having a core of resin and filler, wherein the core is coatedwith resin. In particular, the cured (or partially cured) stream 52 ofcore particles discharges from the curing apparatus 50 and then feedsthe coating apparatus 60. The coating apparatus 60 is typically aprofiled rotating drum or some form of batch mixer. This rotating drumapparatus may have a rotation speed of 16-20 rotations/min. Typically,the second resin stream 61 is preheated to 50-60° C. and sprayed intothe rotating drum apparatus (containing the formed particles) through anozzle with air atomizing. This rotating drum apparatus operates as abatch process with a process time of about 5 to 20 minutes.

[0145] If an Eirich mixer is employed as the coating apparatus, ittypically operates at a vessel rotation speed of 20-40, preferably30-35, rotations/min and a chopper speed of 700-1100, preferably800-1000, rotations per minute with a process time of 2-10 minutes,preferably 2-5 minutes.

[0146] The second binder stream 61 typically contains a solution ofresin, water, and conventional resin additives. The dry weight ratio ofthe binder stream 12 to the second binder stream 61 is about 70 to 60:30to 40. Second stream 61 and stream 52 are preferably fed to the coatingapparatus 60 to provide a weight ratio of second stream resin (on awater free basis) to uncoated proppant particles of about 1 to 10 partsresin:95 parts uncoated proppant particles. The resin in the firstbinder stream 12 may be the same or different from the resin in thesecond binder stream 61. Alternatively, when a proppant having curableresin in its core is desired, the oven 50 may be operated to merely drythe coated proppant.

[0147] Preferably, stream 16 is fed to a refining apparatus (not shown)such as refining apparatus 15 of FIG. 2 prior to curing/drying inapparatus 50.

[0148] The coated proppant discharges from the coating apparatus 60 asthe coated proppant stream 62 and then feeds the curing apparatus 70.

[0149] The curing apparatus 70 is typically a chamber dryer which heatsthe proppant from a temperature of about 120° to about 180° C. on flatplates (or it may be a rotary drier). The curing apparatus 70 maintainsthe coated proppant at a suitable curing temperature, for example about120° to about 180° C. for a suitable curing time, for example about 1minute to about 2 or more hours. If a proppant having a curable coatingis desired, then curing apparatus 70 is operated to dry, or partiallycure, the coating. The cured proppant is discharged from the curingapparatus 70 as a cured proppant particle stream 72 which is sieved in asieving apparatus 80 to recover a proppant product stream 82 of apredetermined particle size range. A typical predetermined particle sizerange is about 20 to about 40 mesh. A typical sieving apparatus 80 is avibration sieve. Particles having a size outside the predeterminedparticle size are discharged as stream 84.

[0150]FIG. 4 generally shows the process of FIG. 3 with a recycle step.The granulated material is discharged from the granulator 10 as stream16 and may pass to an curing apparatus 20 to at least partially cure thematerials to withstand screening. Curing apparatus 20 is a chamber dryeroperating at a temperature of about 120° to 180° C. for a timesufficient to remove water to be dry enough that the particles do notstick together. Typical times range from about 1 minute to 2 hours. Aswith the process of FIG. 3, a refining step may further be employed onstream 16.

[0151] Dried granulated material stream 22 is then fed to a sieve 30. Atypical sieve 30 is a vibrating screen. Sieved particles ofpredetermined mesh size range are discharged as a sieved stream 32.Particles of a size larger than the predetermined mesh size range aredischarged as a first recycle stream 34 which is sent to a crusher 40and then is recycled to the granulator 10. A typical predetermined meshsize for these core particles is about 8 to about 20 mesh. Anothertypical desired size range is 20 to 40 mesh. Particles of a size smallerthan the predetermined size are recycled to the granulator 10 as asecond recycle stream 36.

[0152] Sieved stream 32 passes to the curing apparatus 50. Curingapparatus 50 may be a chamber dryer which cures the material on flatplates and operates at a temperature of 120° to 200° C., preferably 150°to 190° C., for a time to produce a desired degree of curing. Typicalcuring time ranges from 1 minute to 2 hours. However, this curing stepmay be omitted, and the particles merely dried, if the particles ofsieved stream 32 have the sufficient degree of (or lack of) curing. Thecured (or partially cured) stream 52 of proppant particles dischargesfrom the curing apparatus 50 and then feeds the coating apparatus 60. Anexample of starting material for operation of the process of FIG. 4 maybe summarized as shown by TABLE 1 to make a composite particle. However,the resulting composite would have too high a density to be within thepresent invention. Thus, the ingredients could be changed bysubstituting a low density filler, e.g., hollow glass microspheres, forsome or all of the nepheline syenite to achieve the desired low densitycomposite particle of the present invention. TABLE 1 Starting materialsfiller: Nepheline syenite d_(p) = 8 μm; ρ = 2.65 g/cm³ binder/coating:Resole resin* ρ = 1.23 g/cm³ Composition weight percent weight percentvolume percent (solvent included (solvent free (solvent included basis)basis) basis) Resole resin filler resole filler Resole resin fillerpregranulate 16 84 12.1 87.9 29.1 70.9 of Eirich- mixer product after 2080 15.3 84.7 35   65   coating

[0153] Typical operation of the process of FIG. 4 is summarized as shownby TABLE 2. TABLE 2 mixing/granulation Eirich-mixer R02 (Lab scaleequipment) equipment composition 84 wt. % filler, 16 wt % Resole resinon a solvent included basis processing batch process mixing time 2 min(vessel 64 min⁻¹, chopper 1500 min⁻¹) granulation time 3-5 min (vessel32 min⁼¹, chopper 1500 min⁻¹) moisture correction (depending on particlesize of filler by adding of water or filler; Rule: higher moisture =greater grains visual process controlling on samples for grainsize/granulation time drying equipment chamber dryer/rotating kilnprocessing 60° C./1 hour sieving equipment vibration sieve processing18/30 mesh curing equipment chamber dryer processing heating 120-160°C./1 min. to 2 hours 180° C./1 min. to 2 hours material on flat platescoating equipment rotating plate or Eirich mixer composition 5 wt. %Resole resin on a solvent included basis, 95 weight percent granulateprocessing batch process a) rotating plate TR10  rotation 16-20 min⁻¹ preheating resole resin 50-60° C.  nozzle with air atomizing  processtime 10 min b) Eirich mixer R02  vessel 32 min⁻¹  chopper 900 min⁻¹preheating resole resin 50-60° C. liquid dosage in the batch processtime 3 min curing equipment chamber dryer/rotating kiln processing 180°C./1 min. to 2 hours heating 120-180° C./1 min. to 2 hours material onflat plates sieving equipment vibration sieve processing 18/30 mesh

[0154] Proppants may also be made by modifying the above processes byextruding pellets in an extruder and then mechanically making thepellets spherical (rather than granulating spherical pellets in anEirich mixer.

[0155] C. Urethane Resins

[0156] Polyurethane resins are made by mixing a polyisocyanatecomponent, a polyhydroxy component and a catalyst. Typically thepolyhydroxy component is a polyhydroxy phenolic component dissolved insolvent. Generally the solvents are mixtures of hydrocarbon and polarorganic solvents such as organic esters. Exemplary hydrocarbon solventsinclude aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, high boiling aromatic hydrocarbon mixtures, heavy naphthas andthe like.

[0157] 1. The Polyhydroxy Component

[0158] The polyhydroxy component is generally a phenolic resole resin oralkoxy modified resole resin as described above.

[0159] 2 . Isocyanates

[0160] The isocyanate component which can be employed in a binderaccording to this invention may vary widely and has a functionality of 2or more. As defined herein, polyisocyanates include isocyanates havingsuch functionality of 2 or more, e.g., diisocyanates, triisocyanates,etc. Exemplary of the useful isocyanates are organic polyisocyanatessuch as tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, andmixtures thereof, particularly crude mixtures thereof that arecommercially available. Other typical polyisocyanates includemethylene-bis-(4-phenyl isocyanate), n-hexyl diisocyanate,naphthalene-1,5-diisocyanate, cyclopentylene-1,3-diisocyanate,p-phenylene diisocyanate, tolylene-2,4,6-triisocyanate, andtriphenylmethane-4,4′,4″-triisocyanate. Higher isocyanates are providedby the liquid reaction products of (1) diisocyanates and (2) polyols orpolyamines and the like. In addition, isothiocyanates and mixtures ofisocyanates can be employed. Also contemplated are the many impure orcrude polyisocyanates that are commercially available. Especiallypreferred for use in the invention are the polyaryl polyisocyanateshaving the following general Formula III:

[0161] wherein R is selected from the group consisting of hydrogen,chlorine, bromine, and alkyl groups having 1 to 5 carbon atoms; X isselected from the group consisting of hydrogen, alkyl groups having 1 to10 carbon atoms and phenyl; and n has an average value of generallyabout 0 to about 3. The preferred polyisocyanate may vary with theparticular system in which the binder is employed.

[0162] 3. Coupling Agents

[0163] In the practice of this invention with urethanes, coupling agentsmay be employed. Such coupling agents include, for example, organosilanes which are known coupling agents. The use of such materials mayenhance the adhesion between the binder and the filler. Examples ofuseful coupling agents of this type include amino silanes, epoxysilanes, mercapto silanes, hydroxy silanes and ureido silanes.

[0164] 4. Catalysts

[0165] The above-described isocyanate and/or below-described epoxycompositions are cured by means of a suitable catalyst. The catalystemployed is generally a volatile catalyst or a liquid catalyst. At leastenough catalyst is employed to cause substantially complete reaction ofthe polyhydroxy phenolic resin component and the isocyanate componentand/or cure the epoxy.

[0166] Preferred exemplary curing catalysts are volatile basiccatalysts, e.g., tertiary amine gases, which are passed through a massof core particles being formed or coated, with an inert carrier such asair or carbon dioxide. Exemplary volatile tertiary amine catalysts whichresult in a rapid cure at ambient temperature that may be employed inthe practice of the present invention include trimethyl-amine,triethylamine and dimethylethylamine and the like.

[0167] Exemplary liquid tertiary amines which are basic in natureinclude those having a pKb value in a range of from about 4 to about 11.The pKb value is the negative logarithm of the dissociation constant ofthe base and is a well-known measure of the basicity of a basicmaterial. The higher the number is, the weaker the base. Bases fallingwithin the mentioned range are generally, organic compounds containingone or more nitrogen atoms. Preferred among such materials areheterocyclic compounds containing at least one nitrogen atom in the ringstructure. Specific examples of bases which have a pKb value within therange mentioned include 4-alkyl-pyridines wherein the alkyl group hasfrom 1 to 4 carbon atoms, isoquinoline, arylpyridines, such as phenylpyridine, acridine, 2-methoxypyridine, pyridazines, 3-chloropyridine,and quinoline, N-methylimidazole, N-vinylimidazole, 4,4-dipyridine,phenylpropylpyridine, 1-methylbenzimidazole and 1,4-thiazine. Additionalexemplary, suitable preferred catalysts include, but are not limited to,tertiary amine catalysts such as N,N-dimethylbenzylamine, triethylamine,tribenzylamine, N,N-dimethyl-1,3-propanediamine,N,N-dimethylethanolamine and triethanolamine. It is to be understoodthat various metal organic compounds can also be utilized alone ascatalysts or in combination with the previously mentioned catalyst.Examples of useful metal organic compounds which may be employed asadded catalytic materials are cobalt naphthenate, cobalt octate,dibutyltin dilaurate, stannous octate and lead naphthenate and the like.When used in combinations, such catalytic materials, that is the metalorganic compounds and the amine catalysts, may be employed in allproportions with each other.

[0168] The liquid amine catalysts, if desired, can be dissolved insuitable solvents such as, for example, the hydrocarbon solventsmentioned hereinabove. The liquid amine catalysts are generally employedin a range of from about 0.5% to about 15% by weight, based on theweight of the phenolic resin component present in a composition inaccordance with the invention.

[0169] The curing time can be controlled by varying the amount of liquidcatalyst added. In general, as the amount of catalyst is increased, thecure time decreases. Furthermore, curing takes place at ambienttemperature without the need for subjecting the compositions to heat, orgassing or the like. However, if desired preheating of the filler may beemployed to raise the temperature of the filler to accelerate thereactions and control temperature and thus, provide a substantiallyuniform operating temperature on a day-to-day basis. The filler may betypically preheated to from about 30° F. up to as high as 120° F. andpreferably up to about 75° F. to 100° F. However, such preheating isneither critical nor necessary in carrying out the practice of thisinvention.

[0170] 5. Employing the Urethane-Containing Resin to Make or Coat Cores

[0171] In general, a process for making cores in accordance with thisinvention comprises admixing filler with at least a binding amount ofthe polyhydroxy component. The polyhydroxy component, e.g., resoleresin, is dissolved in sufficient solvent to reduce the viscosity of thephenolic resin component to below about 1000 centipoises. This solventcomprises hydrocarbon solvents, polar organic solvents and mixturesthereof. Then, an isocyanate component, having a functionality of two ormore, is added and mixing is continued to uniformly blend the fillerwith the phenolic resin and isocyanate components. A sufficient amountof catalyst is added to substantially and completely catalyze thereaction between the components. The admixture is cured forming thecores.

[0172] There is no criticality in the order of mixing the constituentswith the filler. On the other hand, the catalyst is typically added tothe mixture as the last constituent of the composition so that prematurereaction between the components does not take place. As a practicalmatter, the polyhydroxy component can be stored separately and mixedwith solvent just prior to use of or, if desirable, mixed with solventand stored until ready to use. Such is also true with the isocyanatecomponent. As a practical matter, the polyhydroxy and isocyanatecomponents should not be brought into contact with each other untilready to use to prevent any possible premature reaction between them.The components may be mixed with the filler either simultaneously or oneafter the other in suitable mixing devices, such as mullers, continuousmixers, ribbon blenders and the like, while continuously stirring theadmixture to insure uniform mixing of the components.

[0173] When the admixture is to be cured with a gaseous catalyst, theadmixture after shaping to form uncured cores is subjected to gassingwith vapors of an amine catalyst. Sufficient catalyst is passed throughthe admixture to provide substantially complete reaction between thecomponents.

[0174] When a polyurethane coating on the cores is to be cured with agaseous catalyst, after the polyhydroxy and polyisocyanate componentsare coated onto the cores then the gaseous catalyst is applied.

[0175] In contrast, liquid catalyst for curing the polyurethane used asa binder for the cores is generally added to the filler material withthe phenolic and isocyanate components to form an admixture. Theadmixture is then shaped into cores and permitted to cure until reactionbetween the components is substantially complete. On the other hand, thecatalyst may also be admixed with either one of the components prior tomixing the filler with the phenolic and isocyanate components.

[0176] Liquid catalyst for coating the cores is generally coated ontothe cores with the phenolic and isocyanate components. The coatings arethen permitted to cure until reaction between the components issubstantially complete. On the other hand, the catalyst may also beadmixed with the phenolic prior to coating the cores with the isocyanatecomponents.

[0177]FIG. 7 shows a process flow diagram of a cold set process formaking cores and coating cores with polyurethane.

[0178] Phenolic component stream 202 and catalyst stream 204 feed amixer 200 wherein they are mixed to produce a mixture stream 206. Themixture stream 206 and a filler stream 212 feed a pre-mixer 210operating at 50 to 80 revolutions per minute (rpm) to form a mixedstream 214.

[0179] Mixed stream 214 and an isocyanate stream 222 feed an Eirichmixer 220 operating at high speed. The resin cures in the Eirich mixer220 to form cores of filler and cured resin which discharge as a corestream 224. Optionally, the core stream 224 feeds a fluid bed drier 230.In the fluid bed drier 230 the cores are dried using ambient to 50° C.air from air stream 236 to remove excess solvent and/or assist setting.This produces a stream of dried cores 234. If coated cores are desired,the cores 234 feeds standard foundry mixer 240 operating at 50 to 80rpm. A phenolic component 242 and catalyst stream 244 and an isocyanatecomponent stream 245 also feed the standard foundry mixer 240, to coatthe cores and then cure on the cores. This forms a stream of curedcoated cores 246 which feeds an optional fluid bed dryer 250. Dryer 250dries the cured coated cores using ambient to 50° C. air stream 252 toremove excess solvent. This produces a proppant stream of dried coatedcores 254.

[0180] If desired, the premixing at 50 to 80 rpm and the high speedmixing may be accomplished in the same Eirich mixer 220 by controllingfeed rates and mixing speed. For example, the filler stream 212 andphenolic/catalyst resin stream may be fed to the mixer operating at lowspeed of 50 to 80 rpm. Then the isocyanate stream 222 would feed theEirich mixer operating at high speed.

[0181] Also, urethane binders typically have a curing exotherm whichincreases its temperature during curing. This higher temperatureincreases curing speed. If additional curing is desired, a small amount(less than 3 wt. %) of hot catalyst or hardener may be added duringmixing.

[0182] 5. SIGMA SET Binders

[0183] A preferred class of polyurethane binders are SIGMA SET resins.These are phenolic resin dissolved in petroleum solvents which arecross-linkable with a polymeric isocyanate using an amine catalyst. Theyare available from Borden, Inc., Louisville, Ky. A typical blend forcoating composite proppant provides 1000 lbs of cores coated with a 10weight percent coating of a mixture of 60 pounds of SIGMA CURE MR71, 40pounds of SIGMA SET 6605 and 2 pounds of SIGMA SET 6710 available fromBorden, Inc., Louisville, Ky. Typically, the SIGMA SET 6710 is mixedwith SIGMA CURE MR71 before use.

[0184] D. Epoxy Resin

[0185] Epoxy resins are commercially available and prepared from eitherglycidyl materials such as the ethers, produced by the reaction ofchlorohydrin with a phenol or alcohol, or epoxies, such as the productfrom the reaction of peracetic acid with a linear or cycloaliphaticolefin. The epoxy resin molecule is characterized by the reactive epoxyor ethoxline groups:

[0186] which serve as terminal linear polymerization points.Crosslinking or cure is accomplished through these groups or throughhydroxyls or other groups present. The well-known epoxy resins areusually prepared by the base-catalyzed reaction between an epoxide, suchas epichlorohydrin and a polyhydroxy compound, such as bisphenol A.

[0187] Preferably epoxy resins can be selected from glycidyl ethers madefrom bisphenol A and epichlorohydrin. These resins are available inliquid form having a typical viscosity of about 200 to about 20,000centipoises, and an epoxide equivalent weight of about 170 to about 500and weight average molecular weight of about 350 to about 4000. Typicalepoxy resins include ARALDITE 6005 sold by Ciba-Geigy Corporation or EPN1139 novolac-based epoxy resin such as a liquid epoxy novolac resinmanufactured by Ciba-Geigy Corporation. A preferred epoxy resin is DowDER 331 manufactured by Dow Chemical Company, Midland, Mich. However,solid epoxy resins (solid in the neat state) may be employed if they aresoluble in the binder/coating resin system and reactive.

[0188] In general, preferred bisphenol A-based epoxy resin for thepresent invention would have approximately the structure given inFormula V below. These types of resins are commercially available in arange of molecular weights, epoxy equivalents, and viscosities.Typically, these epoxy resins are reaction products of bisphenol A andepichlorohydrin as shown, for example, by Formula V:

[0189] The reaction products polymerize to form resins having thefollowing general Formula VI:

[0190] In Formula VI, n is the number of repeating units and may be from0 to about 15. Although the preferred formulation employs the above typeof epoxy, other epoxy resins are useful. These would include any epoxyresins that are at least di-functional and soluble in the resin system.The upper limit of functionality occurs where the epoxy is insoluble, orintractable, in the resin system. The resin system would include thebase resin and the solvents and plasticizers the base resin is dissolvedinto. The two parameters, functionality and solubility, are key to theapplication for improved resistance to water-based coatings. If an epoxyresin is soluble in the resin system, and if it is “cross-linkable”(minimally di-functional), then the properties disclosed relative toresistance to water-based coatings would be attainable in varyingdegrees.

[0191] The epoxy resin is uncured when added to the binder/coating resinsystems of the present invention. The epoxy resin is then cured. Epoxyresins may be cross-linked by various routes, and the resin systemspresently disclosed provide several of these routes. Epoxy-epoxypolymerizations initiated by tertiary amines, for example, are wellknown mechanisms in the field of epoxy chemistry. Such tertiary aminesare described above as catalysts for curing polyurethane resins.Epoxy-hydroxyl polymerization may occur if properly catalyzed. Bothorganic and inorganic bases have been used as catalysts forepoxy-hydroxyl polymerization. A tertiary amine is one such catalyst. Itshould also be apparent to one skilled in the art that heat will aid thepolymerizations discussed herein.

[0192] A process for making the composite proppants of the presentinvention with filler and epoxy resin would be similar to that describedabove for making composite proppants with filler and polyurethane resin.

[0193]FIG. 8 shows a process flow diagram of a cold set process formaking cores and coating cores with an epoxy resin.

[0194] Epoxy stream 302 and filler stream 312 feed a premixer 310operating at 50 to 80 revolutions per minute (rpm) to form a mixedstream 314.

[0195] Mixed stream 314 and catalyst stream 322 feed an Erich mixer 320operating at high speed. The resin cures in the Erich mixer 320 to formcores of filler and cured resin which discharge as a core stream 322.Optionally, the core stream 322 feeds a fluid bed drier 330. In thefluid bed drier 330 the cores are dried using ambient to 50° C. air fromair stream 336 to remove excess solvent and/or assist setting. Thisproduces a stream of dried cores 334.

[0196] If coated cores are desired, the cores 334 feed a standardfoundry mixer 340 operating at 50 to 80 rpm. An epoxy stream 342 and acatalyst stream 344 feed the standard foundry mixer 340, to coat thecores and then cure. This forms a stream of cured coated cores 346 whichfeeds an optional fluid bed dryer 350. Dryer 350 dries the cured coatedcores using ambient to 50° C. air stream 352 to remove excess solvent.This produces a proppant stream of dried coated cores 354. If desired,the fluid bed dryer could be omitted or replaced by a rotary dryer or achamber having an inclined, vibrating perforated plate with hot air indownflow, e.g., a WOLVARINE dryer.

[0197] As in the case of the urethanes, the premixing step 310 and highspeed mixing can both be performed in the Erich mixer 320 by adjustingits speed.

[0198] If coatings are not desired, the coating step in mixer 340 andthe drying step in dryer 350 are omitted.

[0199] The stream 354 is typically sent to classification to collectproppants having the desired particle size. Particles which are toosmall may be recycled to the premixer 310. Particles which are too largemay be crushed and then recycled to the pre mixer 310.

[0200] If desired, epoxy groups may be used to modify other groups suchas phenolics to produce an epoxy modified phenolic resin.

[0201] E. Furans

[0202] Furans employable in the present invention include resins madefrom urea formaldehyde and furfuryl alcohol; urea formaldehyde, phenolformaldehyde and furfuryl alcohol; phenol formaldehyde and furfurylalcohol; or formaldehyde and furfuryl alcohol.

[0203] Suitable furan resin for use as a binder or coating for the coresof the present invention is disclosed by U.S. Pat. No. 4,694,905 toArmbruster incorporated herein by reference, or other furan resins knownin the art.

[0204] Accordingly, cores are prepared by mixing uncured thermosettingphenolic resin and uncured thermosetting furan resin or a terpolymer ofphenol, furfuryl alcohol and formaldehyde with filler. The filler may bepreheated to an operating temperature of from 225°- 450° F. The resin isthen added while the filler is being mixed to form the cores. As mixingis continued, the resin cures to produce a free flowing productcomprised of filler and the cured resin.

[0205] The cores may then be coated with the resin by a similarprocedure.

[0206] Although it is possible to employ furans without the use of acatalyst, it is preferred to use a curing catalyst which is sufficientlynon-volatile at the operating temperatures, to accelerate the cure ofthe resin. The curing catalyst can be incorporated into or premixed withthe resin or added to the mixture after the resin has been added. Thepreferred method is to add it to the mixer after the resin has beenadded. The advantage of the catalyst is that its use can result in alower coating temperature and/or faster processing time.

[0207] The catalyst can be used as is or dissolved in water or othersuitable solvent system depending on the catalyst. A strong acidcatalyst must be diluted with water to prevent localized reaction of thecatalyst with the resin before the catalyst has had a chance to mix withthe resin. Solid catalysts that do not melt below the mixing temperatureare preferably used in aqueous solution. Catalyst may also be generatedin situ.

[0208] Specific catalysts include acids with a pKa of about 4.0 orlower, such as phosphoric, sulfuric, nitric, benzenesulfonic,toluenesulfonic, xylenesulfonic, sulfamic, oxalic, salicylic acid, andthe like; water soluble multivalent metal ion salts such as the nitratesor chlorides of metals including Zn, Pb, Ca, Cu, Sn, Al, Fe, Mn, Mg, Cdand Co; and ammonia or amine salts of acids with a pKa of about 4.0 orlower, wherein the salts include the nitrates, chlorides, sulfates,fluorides, and the like. The preferred class of catalyst is the ammoniasalts of acids and the preferred catalyst is aqueous ammonium nitrate.

[0209] The amount of catalyst used can vary widely depending on the typeof catalyst used, type of resin used, mixing temperature and type ofmixer. In general, the amount of catalyst solids can range from about0.2% to 10% based on the weight of the resin.

[0210] It is desirable to add a lubricant to the mix at some point afterthe catalyst is added and before the product “breaks down” into freeflowing particles. The lubricant is preferably one that is liquid at themixing temperature and has a sufficiently high boiling point so that itis not lost during the mixing process. Suitable lubricants includevegetable oil, e.g., soy or corn oil, low vapor pressure lubricatingoil, liquid silicone such as Dow Corning Silicone 200, mineral oil,paraffin wax, petrolatum, or the synthetic lubricant ACRAWAX CT (abis-stearamide of a diamine, available from Glyco Chemicals, Inc.,Greenwich, Conn.).

[0211] It is also desirable to include a silane additive to ensure goodbonding between the resin and the particulate matter. The use oforganofunctional silanes as coupling agents to improve interfacialorganic-inorganic adhesion is especially preferred.

[0212]FIG. 9 shows a process flow diagram of a cold set process formaking cores and coating cores with a furan resin of formaldehyde andfurfuryl alcohol.

[0213] Filler stream 402 and liquid acid stream 404 feed an Eirich mixer400 wherein they are mixed to produce a slurry stream 406. The slurrystream 406 and a furan resin (of formaldehyde and furfuryl alcohol)stream 412 feed an Eirich mixer 420 operating at high speed. The resincures in the Eirich mixer 420 to form cores of filler and cured resinwhich discharge as a core stream 424. Optionally, the core stream 424feeds a fluid bed dryer 430. In the fluid bed dryer 430 the cores aredried using ambient to 50° C. air from air stream 432 to remove excesssolvent and/or assist setting. This produces a stream of dried cores434. If desired, an endless belt (not shown) with an overhead heater maybe substituted for the fluid bed dryer (430).

[0214] If coated cores are desired, the cores 434 feed a standardfoundry mixer 440 operating at 50 to 80 rpm. A furan resin (offormaldehyde and furfuryl alcohol) stream 442 and a hydrogen peroxidestream 444 feed the standard foundry mixer 440, to coat the cores. Thisforms a stream of uncured coated cores 446. The core stream 446 and agaseous stream of SO₂ 452 feed a mixer 450. In the mixer 450 the SO₂ andhydrogen peroxide form sulfuric acid in situ and the sulfuric acid curesthe resin. This results in a proppant stream 454 of cured coated cores.If desired, proppant stream 454 may feed an optional dryer (not shown)which dries the cured coated cores using ambient to 50° C. air stream toremove excess solvent or to a dryer (not shown) comprising endless beltswith an overhead infrared heater. The proppant stream may also be sieved(not shown) to recover the desired size particle with the remainderrecycled.

[0215] F. Alkaline-modified Resoles Set by Esters

[0216] Alkaline-modified resoles settable by esters, e.g., ALPHASETresins available from Borden Inc., Louisville, Ky. are disclosed by U.S.Pat. No. 4,426,467 and Re. 32,812 (which is a reissue of U.S. Pat. No.4,474,904), all of which are incorporated herein by reference.

[0217] Typical alkaline-modified resoles settable by esters comprises anaqueous solution, having a solids content of from 50% to 75% by weight,of a potassium alkali-phenol-formaldehyde resin having the followingcharacteristics:

[0218] (a) a weight average molecular weight (M_(w)) of from 700 to2000;

[0219] (b) a formaldehyde:phenol molar ratio of from 1.2:1 to 2.6:1; and

[0220] (c) a KOH:phenol molar ratio of from 0.5:1 to 1.2:1;

[0221] The resins used in this invention are potassium alkalinephenol-formaldehyde resins by which is meant that the alkali in theresin is potassium alkali. This alkali can be present in the resinduring manufacture or, more usually, post added to resin as KOH,preferably in aqueous solution of suitable strength. The alkalinity ofthe resin is expressed in terms of its KOH content and specifically bythe molar ratio of KOH to the phenol in the resin.

[0222] The molar ratio of KOH:phenol in the resin solution is in therange 0.5:1 to 1.2:1 and preferably 0.6:1 to 1.2:1. At ratios less than0.5 the speed of cure and product strength are much reduced. The use ofKOH:phenol ratios lower than 0.6 is not preferred with resins havingM_(w) (weight average) less than 800 because the speed of cure andproduct strength is below optimum.

[0223] If desired, rather than using only potassium hydroxide as a base,the base may be selected from the group of potassium hydroxide, sodiumhydroxide, lithium hydroxide, or mixtures thereof.

[0224] The resins used have a formaldehyde to phenol molar ratio of from1.2:1 to 2.6:1. Especially, within the preferred limits of this ratiosuitable highly condensed resins, with low levels of unreactedformaldehyde and high reactivity can be obtained.

[0225] The curing catalyst used in the invention is an ester. Suitableesters include low molecular weight lactones, e.g., gamma-butyrolactone,propiolactone, and xi-caprolactone, and esters of short and mediumchain, e.g., C₁ to C₁₀ alkyl mono- or polyhydric alcohols, with short ormedium chain, e.g., C₁ to C₁₀ carboxylic acids especially acetic acid,or triacetin (glyceryl triacetate).

[0226] The amount of catalyst used is in the range 20% to 110%,preferably 25% to 40% by weight on the weight of resin solution used,corresponding approximately to 10% to 80% by weight on the weight ofsolid resin in the solution. The optimum in any particular case willdepend on the ester chosen and the properties of the resin.

[0227] A silane, typically delta-aminopropyltriethoxy silane, isincluded in the mixture to improve product strength. Typical amountsrange from 0.05% to 3% by weight on the weight of resin solution.

[0228]FIG. 10 shows a process flow diagram of a cold set process formaking proppant particles of filler and ALPHASET resin binder andALPHASET resin coating.

[0229] In the process an ester stream 502 and filler stream 504 feed amixer 500 operating at 50 to 80 revolutions per minute (rpm) whereinthey are mixed to produce a mixture stream 514. The mixture stream 514and an alkaline modified resole resin stream 522 feed an Eirich mixer520 operating at high speed. (If desired, mixer 500 and mixer 520 may beone Eirich mixer wherein the filler and ester are added at low speed andthe alkaline modified resole resin is then added while mixing at highspeed.)

[0230] The resin cures in the Eirich mixer 520 to form cores of fillerand cured resin which discharge as a core stream 524. Optionally, thecore stream 524 feeds a fluid bed drier 530. In the fluid bed drier 530the cores are dried using ambient to 50° C. air (typically 40° C. air)from air stream 532 to remove excess solvent and/or assist setting,i.e., curing. This produces a stream of dried cores 534.

[0231] If coated cores are desired, a stream of ester 536 and a streamof alkaline modified resole are fed to a mixer 542 where they are mixedto form a stream 544 of curable resin. Both the stream of the cores 534and resin 544 feed standard foundry mixer 540 operating at 50 to 80 rpmwherein the resin coats the cores and then cures. This forms a stream ofcured coated cores 546 which feeds a fluid bed dryer 550. Dryer 550dries the cured coated cores using ambient to 50° C. air stream 552 toremove excess solvent. This produces a proppant stream of dried coatedcores 554.

[0232] If desired, cores 554 are sieved (not shown) to recover thedesired size particles with the remainder recycled.

[0233] G. Melamine/Formaldehyde Resins

[0234] Typically, mixtures of resoles and melamines are heated to effecta melamine formaldehyde reaction to produce a dissolved methylolmelamine reaction product (See U.S. Pat. No. 4,960,826). Heat may beapplied to thermally set (polymerize) these types of conventional resoleresins in curing operations by condensing methylol groups in the resoleresins and condensing methoxy methyl groups in the melamine resins. Theterms melamine resin is a general term to encompass any melamine-formaldehyde resin with or without other ingredients, e.g., urea groups.

[0235] The term “A-stage” resin or dispersion means the resin ordispersion when it is made in solution prior to mixing with a substrate.The term “B-stage” resin or dispersion means the resin or dispersionmixed with substrate.

[0236] A typical melamine phenolic resin for use in binding cores orcoating cores comprises a liquid alkaline resole resin composition aredisclosed by U.S. Pat. Nos. 5,296,584, 5,952,440 and 5,916,966 toWalisser incorporated herein by reference.

[0237] The alkaline resole resins employed as part of the presentinvention may be any of the wide variety of commercially availableaqueous or solvent-based phenolic resole resins. Liquid or solidphenolic resole resins, or mixtures thereof, are operative herein, withliquid resins being preferred.

[0238] The term “melamine crystal” means melamine, per se, andunderivatized in powder, crystalline, or flake form. This shall include,for example, and not by way of limitation, MCI's GP (General Purpose),non-recrystallized grade of melamine powder. Melamine crystal hereinshall also mean 1,3,5-triazine-2,4,6-triamine;2,4,6-triamino-S-triazine; and cyanurotriamide.

[0239] A typical melamine resin is provided as a dispersion comprising(i) the reaction product of combining formaldehyde and phenol at aformaldehyde to phenol mole ratio of about 0.5:1 to about 3.5:1 in thepresence of a basic catalyst, and (ii) solid melamine crystal dispersedthroughout the resin composition. The melamine crystal to phenol moleratio is from about 0.01:1 to about 1:1. Moreover, the dispersion has afree formaldehyde content of at most about 0.5 weight percent.

[0240] Melamine resins, with or without free methylol groups, may be setby heat. Melamine without free methylol have —OR groups rather than —OHgroups. Thus, for example, the unreacted, uncured, A-stage melaminedispersions can be mixed with filler to form cores, or coated ontocores, by driving off any liquid carrier such as organic solvent orwater, to produce a dry or high solids dispersion in or on the core. Thedispersion can then be heat cured during which the melamine issolubilized in the resole, the components react, and crosslinkingresults in amino methyl linkages.

[0241] It has been found advantageous to acidify the dispersions, to amoderately low pH in the range from about 2.5 to about 6 with anysuitable acid just prior to mixing with the filler or coating onto thecores. The lower the pH, the more melamine-phenol condensation isachieved as opposed to phenol-phenol or methylol phenol condensation.The very low pH (pH below about 2.0) of acid catalyzed condensations ofmethylol phenol is avoided.

[0242] Strong carboxylic acids, such as oxalic acid, may be employed.Strongly acidic monovalent and low molecular weight acids such assulfamic, nitric, or methane sulfonic are preferred acids. An acid witha low molecular weight is preferred because of the presence in theresole resins of the present invention of a large amount of alkali. Thisalkali, used as a catalyst to make the resole resin, requiresneutralization. Thus, a low molecular weight acid is preferred tominimize dilution of the final C-stage polymer matrix with non-polymerforming ingredients (acid-base salts) that might otherwise reduce thestrength and temperature performance properties of the curedcomposition. A “latent acid” (a pH neutral substance that chemicallyreacts, usually with application of heat to form an acidic condition)may also be used. A latent acid such as ammonium sulfate is preferred.

[0243] Thus, after the dispersion has been formed by the mixing step, itis converted to a water soluble A-stage, unreacted, uncured but curablebinder composition by adding to the dispersion an acid such as oxalicacid, sulfamic acid, nitric acid, or methane sulfonic acid in an amountsufficient to drop the pH to a level of from 2.5 to 6. The temperaturewhen the binder/coating and acid are mixed is not sufficient to dissolvethe melamine or to initiate any polymerization between the melamine andthe resole. Then the binder and substrate mixture is heated to cure thebinder.

[0244] The uncured, unreacted resole melamine crystal suspensions, alsoreferred to herein as dispersions, may be applied with any suitablyacidic catalyst directly to filler or cores, through, for example,conventional air atomization nozzles or spinning disc atomizationequipment. The product of the present invention is particularly suitedto higher solid applications in the range of about 10 to about 20percent where quantities of water needed to effect complete dissolutionof the melamine are not available.

[0245] A melamine resin made from melamine which contains free methylolgroups may be cold set with acid. Typically, the acids are one of theaforementioned acids provided in sufficient quantity to cure the resinwithout additional heat.

[0246]FIG. 11 shows a simplified process flow diagram of a firstembodiment of a process for making proppants or filtration media of thepresent invention with melamine/phenol-formaldehyde as a binder and as acoating. In the process, a melamine crystal stream 602 and an alkalineresole resin particle stream 604 are fed to a mixer 600 to prepare ahomogeneous binder stream 606. The binder stream 606 contains resin,water and conventional additives. Coupling agents are also typicaladditives. Acid stream 605, binder stream 606 and a filler stream 607are mixed in a high intensity mixer/granulator 608 to cure the binderand to produce a granulated product stream 616. A typicalmixer/granulator 608 is an Eirich R02 mixer manufactured by EirichMachines, Inc., Gurnee, Ill.

[0247] Typically, the mixer/granulator 608 is operated as a batchprocess as disclosed above.

[0248] The amount of binder (resin) generally comprises about 10 toabout 30, preferably about 10 to about 25, weight percent of the totaldry materials (resin, filler, etc.) fed to the granulator 608. Theamount of binder being a water free value defined as the amount of resinand additives other than water. Typically, the mixing occurs in thepresence of a coupling agent such as gamma/amino propel trimethoxysilane. The coupling agent may be added to the mixer/granulator 608before, or premixed with the binder stream 606. Typically, 0 to 50% ofthe total binder stream 606 is water.

[0249] If necessary, the granulated material stream 616 then passes to acuring apparatus 650. Typically, curing apparatus 650 is a drying ovenoperating at a residence time for the granulated material of about 1minute to about 2 hours, at a temperature of about 90° to about 200° C.,preferably about 150° to about 190° C. This produces a cured granulatedproduct stream 652. These are the proppant cores. These cores may beused as proppant as is, after screening to desired particle size, or maybe coated with additional resin.

[0250] If it is desired to coat the cores withmelamine/resole-formaldehyde binder then the cured core stream 652, amelamine/resole-formaldehyde binder stream 654 and an acid stream 656feed a mixer 660 to produce a coated binder stream 662. The coatedbinder stream 662 then feeds an oven 670 operated at conditions as wasoven (curing apparatus) 650 to cure the coating and produce a proppantstream 672 of cured coated cores. Alternatively, if cold set resins areemployed, the oven may be omitted and the resins may be cold set in themixer 660. Typical cold set resins may be selected from the groupconsisting of melamine which contains free methylol groups and for whichsufficient acid is provided, or other cold set resins, such aspolyurethane.

[0251] The cured granulated product stream 672 feeds a screeningapparatus 680 to recover a proppant product stream 682 of predeterminedproduct size. A typical screening apparatus 680 is a sieve such as avibrating screen. A typical desired proppant particle has a d₅₀ from 0.4to 0.8 mm, or a particle diameter range of 20 to 40 mesh (0.425 to 0.85mm).

[0252] H. Urea/Formaldehyde Resins

[0253] The urea/formaldehyde resins are employed as a binder or coatingby methods similar to those employed for other thermosetting resins. Forexample, they may be combined with particles to form composite cores andthen cured at 150 to 250° C. for 30 to 90 seconds. Likewise, they may becoated onto composite cores and then cured at 150 to 250° C. for 30 to90 seconds.

[0254] The thermosetting urea-formaldehyde (UF) resin can be preparedfrom urea and formaldehyde monomers or from UF precondensates in mannerswell known to those skilled in the art. Skilled practitioners recognizethat the urea and formaldehyde reactants are commercially available inmany forms. Any form which can react with the other reactants and whichdoes not introduce extraneous moieties deleterious to the desiredreaction and reaction product can be used in the preparation ofurea-formaldehyde resins useful in the invention. One particularlyuseful class of UF resins for use in preparing binders in accordancewith the present invention is disclosed in U.S. Pat. No. 5,362,842, thedisclosure of which is incorporated herein by reference.

[0255] Formaldehyde for making a suitable UF resin is available in manyforms. Paraform (solid, polymerized formaldehyde) and formalin solutions(aqueous solutions of formaldehyde, sometimes with methanol, in 37percent, 44 percent, or 50 percent formaldehyde concentrations) arecommonly used forms. Formaldehyde also is available as a gas. Any ofthese forms is suitable for use in preparing a UF resin in the practiceof the invention. Typically, formalin solutions are preferred as theformaldehyde source.

[0256] Similarly, urea is available in many forms. Solid urea, such asprill, and urea solutions, typically aqueous solutions, are commonlyavailable. Further, urea may be combined with another moiety, mosttypically formaldehyde and urea-formaldehyde adducts, often in aqueoussolution. Any form of urea or urea in combination with formaldehyde issuitable for use in the practice of the invention. Both urea prill andcombined urea-formaldehyde products are preferred, such asUrea-Formaldehyde Concentrate or UFC 85. These types of products aredisclosed in, for example, U.S. Pat. Nos. 5,362,842 and 5,389,716.

[0257] Any of the wide variety of procedures used for reacting theprincipal urea and formaldehyde components to form a UF thermosettingresin composition also can be used, such as staged monomer addition,staged catalyst addition, pH control, amine modification and the like.Generally, the urea and formaldehyde are reacted at a mole ratio offormaldehyde to urea in the range of about 1.1:1 to 4:1, and more oftenat an F:U mole ratio of between about 2.1:1 to 3.2:1. Generally, the U-Fresin is highly water dilutable, if not water soluble.

[0258] Many thermosetting urea-formaldehyde resins which may be used inthe practice of this invention are commercially available.Urea-formaldehyde resins such as the types sold by Georgia PacificResins, Inc. (such as GP-2928 and GP-2980) for glass fiber matapplications, also those sold by Borden Chemical Co., and by NestleResins Corporation may be used. These resins are prepared in accordancewith the previous teachings and contain reactive methylol groups whichupon curing form methylene or ether linkages. Such methylol-containingadducts may include N,N′-dimethylol, dihydroxymethylolethylene;N,N′-bis(methoxymethyl), N,N′-dimethylolpropylene;5,5-dimethyl-N,N′dimethylolethylene; N,N′-dimethylolethylene; and thelike.

[0259] Urea-formaldehyde resins useful in the practice of the inventiongenerally contain 45 to 70%, and preferably, 55 to 65% non-volatiles,generally have a viscosity of 50 to 600 cps, preferably 150 to 400 cps,normally exhibit a pH of 7.0 to 9.0, preferably 7.5 to 8.5, and oftenhave a free formaldehyde level of not more than about 3.0%, and a waterdilutability of 1:1 to 100:1, preferably 5:1 and above.

[0260] The reactants for making the UF resin may also include a smallamount of resin modifiers such as ammonia, alkanolamines, or polyamines,such as an alkyl primary diamine, e.g., ethylenediamine (EDA).Additional modifiers, such as melamine, ethylene ureas, and primary,secondary and tertiary amines, for example, dicyanodiamide, can also beincorporated into UF resins used in the invention. Concentrations ofthese modifiers in the reaction mixture often will vary from 0.05 to20.0% by weight of the UF resin solids. These types of modifiers promotehydrolysis resistance, polymer flexibility and lower formaldehydeemissions in the cured resin. Further urea additions for purposes ofscavenging formaldehyde or as a diluent also may be used.

[0261] One example of a cold set process for using UF resin to bind orcoat cores would be similar to that of FIG. 9 for furans.

[0262] I. Polymer/Cement

[0263] A preferred composite particle comprises a polymer, a cement, ahigh density filler, e.g., a filler having a density of 2.45-3.20(preferably 2.50-2.80) grams/cm³, a low density 0.507-1.50 grams/cm³filler, e.g., glass microspheres, fly ash, ground almond shells, groundcoconut shells or ground walnut shells, combined in amounts to result ina composite particle having an overall bulk density of 0.50-1.30grams/cm³ (preferably 0.95-1.10 grams/cm³), as well as a grain densityof 0.90-2.20 grams/cm³ (preferably 1.40-1.60 grams/cm³).

[0264] One such composite employs a polymer/cement binder composition.In general, polymer/cement compositions may contain at least one memberof the group consisting of phenol-aldehyde resin, e.g., uncured resolesor novolacs, melamine-aldehyde resin, urea-aldehyde resin,melamine-urea-aldehyde resin, polyimide resin and polyamide resin.Additives may also be present such as polyamide, glycerol,polyvinylalcohol, plasticizer, adhesion agent, e.g., silanes, and orzinc stearate. Typical polyamides are fatty alcohol soluble polyamidesor polyacrylamides.

[0265] Hydraulic cement used in the polymer/cement may be conventionalcement such as Portland cement (normal Portland cement, high earlystrength Portland cement or moderate Portland cement, for example),microfine cement (e.g., RHEOCEM 650, microfine Portland cement availablefrom MBT (Australia) Pty. Ltd.), blended cement (Portland blast furnacecement, silica cement or fly-ash cement, for example), lime cement,special cement (high alumina cement or oil well cement, for example) andvarious gypsum. One or more kinds of hydraulic cement can be used.

[0266] The polymer resin that generates water when cured may be suitablyformaldehyde resin or polyamide resin. The resin may have apredetermined viscosity adjusted by solvent in view of moldingthereafter. It is theorized that water released by the curing of thepolymer is advantageously taken up by the cement to help minimizeporosity.

[0267] Aldehyde polymer/cement resins are composed of a mixture ofcement, anhydrous aldehyde resin precursor, organic solution agent andadditives. Typical polymer/cement compositions are disclosed by EuropeanPatent application No. 0590948 and U.S. Pat. No. 4,003,878 to Smith.Cement with formaldehyde resin precursor or polyamide precursor asdisclosed by U.S. Pat. No. 5,651,816 to Kobayashi, et al. Cement withmelamine-formaldehyde is disclosed by U.S. Pat. Nos. 4,820,766 toLahalih, et al and 5,478,391 to Bashlykov, et al, all of which areincorporated herein by reference in their entirety.

[0268] The aldehyde resin may be a phenol resin, melamine resin or urearesin, preferably in the form of alcohol solution with a nonvolatilecomponent of 40 to 70%. Alcohol which may be used in this invention ismethanol, ethanol, propanol, butanol, cyclohexanol, phenol, cresol,ethylene glycol, trimethylene glycol or the like.

[0269] The polyamide resin may be preferably in the form of solution forwhich a solvent of N-methyl-2-pyrrolidone or N,N-dimethyl acetamide orthe like is used with a nonvolatile component of 10 to 30% includedtherein.

[0270] The polymer/cement/filler composite particle has at least onekind of hydraulic cement, a polymer precursor that is substantiallyanhydrous and generates water by a curing reaction, and theabove-described filler. The composition comprises 100 parts by weightpowder (powder being cement and filler), 10 to 200 (typically 10 to 100,or 10 to 60, or 12 to 30) parts by weight polymer precursor (preferablyphenol-formaldehyde polymer resin), 0.1 to 12 parts by weight methanolor ethanol, and 0 to 5 parts by weight other additive, e.g.,plasticizer. Of course the relative amounts of cement and polymer must,when combined with filler and optional coating, result in the desiredlow density composite particle. The polymer may be provided in a moltenform or as a solution. The solution agent may be methanol (for phenolicresins) or ethanol.

[0271] The hydraulic cement has filler particles added and is employedto make cores of these composite particles. The blend ratio of polymerresin is relative to 100 weight parts of powder components of hydrauliccement having the filler added.

[0272] The filler particles are typically present in an amount fromabout 3 to about 50 weight percent of the core. Typical subranges areabout 5 to about 25 weight percent or about 5 to about 15 weight percentof the core. However, sufficient low density filler must be present toachieve composite particles of the desired low density, namely,composite particle bulk density of 0.50 to 1.30 gr/cm³, preferably 0.95to 1.10 gr/cm³, and composite particle grain density (particle density)of 0.90 to 2.20 gr/cm³, preferably 1.40 to 1.60 gr/cm³.

[0273] Additive or filler is blended with composite material of polymerresin and hydraulic cement. Such additive or filler may be blended by aconventional mixer such as an Eirich type mixer or a helical mixer. Ifthe blend ratio of polymer precursor is relatively small, it may bepreferably blended by a mixer providing a compression function, shearingfunction or spatula touching function. Such a mixer may be a kneader, awet pan mill, a helical rotor, a roller mill, a Banbury type mixer orthe like.

[0274] Composite material including formaldehyde resin may be heated ata temperature of 100° to 300° C. and preferably at a temperature of 150°to 250° C. Composite material including polyamide precursor may beheated at a temperature of 300° to 500° C. and preferably at atemperature of 350° C. to 450° C. Heating composite material curespolymer precursor and generates water, whereby hydraulic cement hydratesso that the cement product has higher physical strength.

[0275] In general, formaldehyde resin is rapidly cured in an acid areaof less than pH 7, but it will be able to be fully cured even in analkali area of more than pH 7 if it is heated at a temperature of 150°C. to 250° C. for a relatively longer time.

[0276] It is known that the curing reaction of formaldehyde generateswater. The thus generated water hydrates hydraulic cement under heat toproduce a cement hydrate.

[0277] An example of a typical curing reaction of polyamide precursorthat produces polyamide in accordance with an intramolecularcyclodehydration reaction of polyamic acid is as follows:

[0278] Water generated by imide reaction of polyimide precursor hydrateshydraulic cement under heat in the same manner as water generated bycuring reaction of formaldehyde precursor to produce a cement hydrate.

[0279] Although the cement of the invention has no water particularlyrequired on kneading, it may be blended with a small quantity of water.Furthermore, there may be added thereto an additive such as glycerol,glycerol triacetate, polyethylene glycol, furfural, dibutyl phthalate,phthalic anhydride, stearic acid, rosin, polyamide, polyacrylamide,polyvinyl alcohol or the like.

[0280] Particularly, polyamide, polyacrylamide or polyvinyl alcohol is apreferable additive for improvement of the cement product. The additivemay be added directly to the polymer resin and then dissolved ordispersed therein, but it may be dissolved or dispersed in solvent suchas ethanol, methanol or N,N-dimethylacetamide and then added to polymerresin.

[0281] A blend ratio of the additive may be generally of 0.5 to 20weight parts to 100 weight parts of polymer resin and preferably 2 to 12weight parts thereto.

[0282] Polyamide used in the invention is preferably alcohol-soluble.Such alcohol-soluble polyamide may be amide bonding CONH having at leasta part of hydrogen substituted by methoxymethyl group, or amide bondingCON(R) produced from a secondary amine. Such polyamide added to thepolymer precursor reacts with the polymer precursor during heating andcuring in the manner corresponding to that in which formaldehyde resinprecursor or polyimide precursor reacts through intramolecularcyclodehydration under heat.

[0283] Generally, the cement composite material is blended with thefiller when kneaded in the percentages listed above.

[0284] In order to improve adhesion of filler and/or hydraulic cement toresin, there may be added conventional silane coupling agent thereto.Such silane coupling agent may be gamma-aminopropyl triethoxysilane,gamma-ureidopropyl triethoxysilane or gamma-glycidoxypropyltrimethoxysilane.

[0285]FIG. 12 shows a process for making proppant of the presentinvention from cement/phenol-formaldehyde polymer compositions. Aluminacement stream 702, phenol-formaldehyde resin stream 704, additivesstream 706, and a filler particle stream 710 feed a high speed Eirichmixer 700 in which the cement/phenol-formaldehyde resole resin andfiller are mixed and granulated to form a stream of uncured cores 722.The core stream 722 then passes to a curing apparatus 730 which is adrying oven which heats the cores for an appropriate time to atemperature in the range of from 100° C. to 300° C. This cures the resinand generates water to hydrate the cement so that the cement has higherphysical strength. A stream of cured cores 731 is discharged from theoven 730 and passes through an optional screen 732 to produce a stream733 of screened cured cores of desired size and a stream 734 of cores ofundesired size (too large and/or too small, hereinafter termed “off-sizecores”). Stream 734 passes into a grinder mill 736 which grinds the offsize cores to make material stream 738 which is recycled as filler intofiller stream 710.

[0286] If it is desired to coat the screened, cured cores 733, then aresole resin stream 739 and core stream 733 feed a mixer 740 to coat thecores which discharge as coated core stream 742. The coated core stream742 then feeds a drying oven 750 which maintains the coated cores for anappropriate time to a temperature in the range of from 100° C. to 300°C. to cure the coating. The cured coated cores are then discharged asproppant stream 752. The proppants are then screened by a conventionalsieve (not shown) to recover proppant particles of desired size.Particles smaller than the desired size may be recycled (not shown) andparticles larger than the desired size may be crushed and then recycled(not shown). Of course, in the alternative, a cold set resin could beemployed as a coating if desired.

[0287] J. Macro Defect Free (MDF) Cement

[0288] Another composite particle, which comprises a binder of cementand polymer as well as the filler particles in amounts to achieve theabove-described low densities, employs macro defect free (MDF) cement.MDF cement is a cement free from macroscopic defects and is well knownin the art. U.S. Pat. No. 4,070,199 describes an hydraulic materialhaving a high flexural strength, prepared by kneading by means of acylinder mixer a mixture of hydraulic cement, water and a polymersoluble or dispersable in water. The product is then pressed and left toharden. Subsequent patents (EP 55035 and EP 21682) describe otherpolymeric materials which can be included in cement mixtures, such ashydroxypropylmethylcellulose or partially hydrolized polyvinyl acetate.

[0289] The use of fibers in MDF cement matrices is well known in theart. For instance, Italian Patent No. 1,068,427 reports the use ofinorganic mineral fibers (asbestos fibers), organic or polymeric fibers(polypropylene or nylon). According to the '427 Patent, after additionof nylon fibers cut in 20 deniers pieces having a constant length equalto 10 mm, the hardened cement matrix shows a high proportional elasticlimit, which remains substantially equal even when increasing thequantity of fibers up to 6% by weight.

[0290] The term “hydraulic cement” means any material setting andhardening by water addition, and that consequently sets and hardens inthe presence of water. The hydraulic cement may be a silicate basedcement (siliceous) for instance Portland cement, an aluminate basedcement (aluminous), for instance a calcium aluminate based cement, or amixed cement such as a pozzolan. It is also possible to use mixtures oftwo or more different hydraulic cements. According to a preferredembodiment of the invention, aluminate based cements or Portland cementis used.

[0291] Any aggregate, optionally fly ashes and additives for preparingthe mixtures known in the art can be used in the cement material of theinvention. However, sufficient low density filler must be present toachieve composite particles of the desired low density, namely,composite particle bulk density of 0.50 to 1.30 gr/cm³, preferably 0.95to 1.10 gr/cm³, and composite particle grain density (particle density)of 0.90 to 2.20 gr/cm³, preferably 1.40 to 1.60 gr/cm³.

[0292] Practically any commercially available can be used in the cementcompositions of the invention, such as: Portland cement,Portland-composite cement, blast furnace cement, pozzolanic cement andcomposite cement. The cement composition of the invention mustnecessarily comprise an organic polymer soluble or dispersable in water.The polymer is used to give the cement mixture the necessary moldabilitycharacteristic of this kind of cement, and to improve its mechanicalcharacteristics.

[0293] As far as the present invention is concerned, a wide variety ofpolymers soluble or dispersable in water which can be used.

[0294] Examples of polymers soluble or dispersable in water polymerswhich can be suitably used are: alkyl and hydroxyalkyl cellulose ethers(methylcellulose, hydroxyethylcellulose, methylhydroxy ethyl cellulose,ethyl-hydroxyethylcellulose, propylcellulose,hydroxypropylmethylcellulose, hydroxybutylmethylcellulose) acrylamidepolymers or copolymers, (polyacrylamide, polymethacrylamide,acrylamide/methacrylamide copolymer); vinylacetate hydrolizable polymersor copolymers, particularly polyvinylacetate; vinyl alcohol polymers orcopolymers; alkylene oxide polymers (polyalkylene glycols having weightaverage molecular weight above 10,000), or polyalkoxy-derivatives ofalcohols and/or phenols.

[0295] Every polymer soluble or dispersable in H₂O reported in theEuropean Patent No. 280971 can be used in the present invention.According to EP 280971, organic polymers such as water-soluble polymeror water-dispersable polymers in the form of a polymer emulsion or apolymer latex can be used. EP 280971 reports water-soluble polymers suchas water-soluble proteins, water soluble starches, water solublecellulose derivatives (e.g., hydroxypropylmethyl cellulose), partiallyhydrolized polyvinyl acetate, polyvinyl alcohol, polyacrylic soda,polyethylene oxide, polyacrylamide, cross-linked acrylic acid polymer,water-soluble urea resin, water-soluble melamine resin, water-solubleepoxy resin, water-soluble polyester, water-soluble phenol-formaldehyderesin, water-soluble amine neutralization alkyd resin, polyvinylmethylether, polyvinylpyrrolidone, polystyrene sulfonic acid, andquaternary polyvinyl pyridine; and water-dispersable polymers such asthose in the form of rubber latex, acrylic emulsion, vinyl acetateemulsion, vinyl chloride emulsion, ethylene-vinyl acetate emulsion,polypropylene emulsion, epoxy resin emulsion, polyurethane emulsion,polyamide emulsion, or bituminous emulsion.

[0296] The polymer content in the cement mixture can range from about 10to about 40% by weight of the cores, preferably from 10 and 30% byweight. The water amount, even though it can change as a function of thedifferent kind of polymer, is preferably not greater than 30% by weightwith respect to the hydraulic cement amount. Greater water amounts canquickly depress the mechanical characteristics of the final material.

[0297] The filler particles may be present in amounts of from about 45to about 89 weight percent of the cores. Typical filler ranges are fromabout 50 to 89 or 60 to 89 weight percent of the cores. The cement ispresent in an amount of about 1 to about 15 weight percent of the cores.

[0298] The mixtures useful for the preparation of the MDF cement of theinvention have been prepared considering the additional waterrequirement to process a mixture containing reasonable volumes of fillerparticles.

[0299] In the case of MDF Portland cement or aluminous cement, anincrease in water amount of the mixture yields MDF cements having lowermechanical properties (flexural strength about 100 MPa when an aluminousmatrix is used). However, such an increase allows mixtures of MDF cementadded with fillers to be processed in the presence of high volumes ofthe latter. Therefore, the effects of various amounts of added water andfiller should be balanced to achieve desired results.

[0300] A process for making proppant particles of MDF cement is shown byFIG. 13. In the process, a cement stream 802, a water stream 804, aplasticizer stream 806, a filler stream 807, and a water soluble polymerstream 808 feed a planetary mixer 800 to produce a slurry stream 810.The slurry stream 810 feeds a high shear mixer 820, such as a two rollmill, to produce a stream 822. The stream 822 then undergoes acompaction and homogenization phase in an extruder 830.

[0301] The extruder 830 assists in homogenizing the stream 822ingredients to a uniform density. A stream of chopped extruded pellets832 is discharged from the extruder 830. If desired, the extruder may bereplaced by any device which provides suitable compaction andhomogenization to form MDF cement. An example of such devices includes acalendering device (not shown) in which the stream 822 would feedbetween rolls. The rolls would have surface indentations sized to makeand pressurize granules of the stream 822 material.

[0302] The pellet stream 832 from the extruder 830 then passes into anoven 840 for curing. Oven 840 typically operates at a temperature ofabout 50 to 200° C. to produce a stream of cured pellets 842.

[0303] If desired, the pellets of stream 842 may be coated by a resin.One way to accomplish this is to feed pellet stream 842, a cold-settableresin stream 852, and a curing agent stream 853 to a mixer 850. Thisproduces a stream of coated pellets 854 which may be fed to an optionaldryer 860 to produce a coated proppant stream 862.

[0304] K. Employing Both Heat Set and Cold Set Resins

[0305] It is not necessary that the polymer in the core be the same asthe polymer in the coating. Thus, it is desirable to employ a heat setresin, such as a resole, in the core and a cold set resin, such as apolyurethane, in the coating. This has the advantage of fasterprocessing time than a proppant having heat set resins in both the coreand coating.

[0306] It is also possible to employ a cold set resin in the core and aheat set resin in the coating, so long as the cold set core canwithstand the heat set conditions.

[0307] L. Proppant Particle

[0308]FIG. 5 shows a proppant particle 10 comprising filler particles20, and a resin 15.

[0309]FIG. 6 shows a coated proppant particle 110 having a core 112, ofresin 15 and filler particles 24, coated by a second resin coating 25.

[0310] M. Composite Particle Parameters

[0311] The following parameters are useful when characterizing compositeproppant particles, composite gravel packing, and composite filtrationmedia particles of the present invention.

[0312] The composite particles of the present invention have a densitylighter than conventional sand. Sufficient low density filler must bepresent to achieve composite particles of the desired low density,namely, composite particle bulk density of 0.50 to 1.30 gr/cm³,preferably 0.95 to 1.10 gr/cm³. Typically, the proppant particles have acomposite particle bulk density of about 50 to about 80.5 lbs/ft³. Also,the composite particle grain density (particle density) range from 0.90to 2.20 gr/cm³, preferably 1.40 to 1.60 gr/cm³. They generally have asphericity of greater than 0.7, preferably greater than 0.85, and morepreferably greater than 0.9. Generally, the coating is from 0 to about10 weight percent of the total weight of the proppant regardless ofwhether the core binder is a polymer binder or a combination of polymerand cement.

[0313] Where the binder is polymer resin or inorganic binder such asphosphate glass, the volume percent filler particles in the coated oruncoated composite particle is 60 to 85%, preferably about 65 to about85 volume percent, more preferably about 80 to about 85 volume percent;the weight percent filler particles in the composite particles is about45 to about 90%, typically about 45 to about 80% or about 60 to about75% or about 70 to about 90%; and the weight percent filler particles inthe core of the resin coated composite particle is about 50 to about90%, typically about 50 to about 80% or about 65 to about 75% or about80 to about 90%.

[0314] Where the binder is polymer/cement the composition comprises 100parts by weight powder (powder being cement and filler), 10 to 200(typically 10 to 100, or 10 to 60, or 12 to 30) parts by weight polymerprecursor (preferably phenol-formaldehyde polymer resin), 0.1 to 12parts by weight methanol or ethanol, and 0 to 5 parts by weight otheradditive, e.g., plasticizer. The filler particles are typically presentin an amount from about 3 to about 50 weight percent of the core.Typical subranges are about 5 to about 25 weight percent or about 5 toabout 15 weight percent of the core.

[0315] Where the binder is MDF cement, the polymer content in the cementmixture can range from about 10 to about 40% by weight of the cores,preferably from 10 and 30% by weight. The water amount, even though itcan change as a function of the different kind of polymer, is preferablynot greater than 30% by weight with respect to the hydraulic cementamount. Greater water amounts can quickly depress the mechanicalcharacteristics of the final material. The filler particles may bepresent in amounts of from about 45 to about 89 weight percent of thecores. Typical filler ranges are from about 50 to 89 or 60 to 89 weightpercent of the cores. The cement is present in an amount of about 1 toabout 15 weight percent of the cores.

[0316] In general, a preferred embodiment of the composite particles ofthe present invention comprise a cement and a polymer as a binder andemploy higher density filler particles for strength and lower densityfiller particles to help achieve the desired low densities describedabove. The proportions of thse ingredients depends upon the final use ofthe composite particle. For example the strength requirements for aproppant particle are higher than for gravel packing.

[0317] The composite particle d₅₀ ranges from about 0.4 to about 0.8 mm.For coated proppant, wherein the first and second portions of binder arepolymer, the dry weight ratio of the first portion of binder to thesecond portion of binder is 70 to 60:30 to 40. The composite particlesare within a size range from about 4 to about 100 mesh based on U.S.Standard Sieve Series, typically about 8 to about 60 mesh, preferably asize range of a 20/40 material based on API Method RP 56 Section 4(0.425 to 0.85 mm).

[0318] Crush material <6-8% of precured proppants at 4000 psi closurestress is defined as that measured according to the following procedure.American Petroleum Institute Method RP 56 procedure Section 8.

[0319] Dust levels are measured as turbidity by API Method RP 56 Section7.

[0320] Sphericity is determined by API Method 56 Section 5.

[0321] Chemical inertness should be comparable to Jordan silica sand(20/40 mesh) with regard to resistance to hydrocarbons and sodiumhydroxide solution at pH12. Acid resistance is determined by API MethodRP 56 Section 6. The alkali resistance is determined as the resistanceto sodium hydroxide solution at pH 12 and 200° F. for 48 hours. The pHto be kept at 12 by addition of caustic as required. The properties andappearance of the proppant should be kept within acceptable limits whenexposed to aliphatic or aromatic hydrocarbons.

[0322] N. Use of Composite Particles as Proppant or Filtration Media

[0323] The composite particles, as described in this invention havespecial and unique properties such as controlled plasticity andelasticity behavior. Because of these unique properties, the compositeparticles can be applied as the sole proppant in a 100% proppant pack(in the hydraulic fracture) or as a part replacement of existingcommercial available ceramic and/or sand-based proppants, resin-coatedand/or uncoated, or as blends between those, e.g., composite particlesare 10 to 50 weight % of the proppant injected into the well. Thecomposite particles can also be employed as the sole media in a 100%filtration pack or blended with other filtration media.

[0324] When the method of the present invention employs a proppanthaving a precured resin composition, the proppant is put into thesubterranean formation without a need for additional curing within theformation.

[0325] When the method employs a proppant having a curable resincomposition, the method may further comprise curing the curable resincomposition by exposing the resin composition to sufficient heat andpressure in the subterranean formation to cause crosslinking of theresins and consolidation of the proppant. In some cases an activator canbe used to facilitate consolidation of curable proppant. In anotherembodiment employing a curable resin composition on the proppant, themethod further comprises low temperature acid catalyzed curing attemperatures as low as 70° F. An example of low temperature acidcatalyzed curing is disclosed by U.S. Pat. No. 4,785,884 incorporatedherein by reference in its entirety.

[0326] Also, resin-containing particulate material may be used byfilling a cylindrical structure with the resin-containing particulatematerial, i.e., proppant, and inserted into the wellbore. Once in place,the improved properties of this invention are beneficial because theproppant will cure and act as a filter or screen to eliminate thebackwards flow of sand, other proppants, or subterranean formationparticles. This is a significant advantage to eliminate the back flow ofparticulates into above ground equipment.

[0327] The present composite particles are especially advantageous dueto their roundness. This enhances conductivity whether the particles areused alone as a proppant, or together with other proppants, inmulti-layer packs. Multi-layer packs by definition are not the partialmonolayers used in U.S. Pat. No. 3,659,651. In partial monolayers thereare particles in the well that touch the fracture walls, but do nottouch each other. In contrast, in multi-layer packs the proppant fillsthe fractures and production is through the porosity of the proppant.

[0328] O. Use of Composite Particles as Gravel Packing

[0329] It is known that oil or gas well boreholes are provided withgravel packing about their bore holes. Another aspect of the presentinvention is that these gravel packs may be provided with the compositeparticles, or a mixture of gravel and the composite particles, of thepresent invention. These composite particles would be provided in thestandard sizes known for gravel used in gravel packs. The gravel packsmay typically comprise from about 5 to about 50 weight percent coated oruncoated composite particles. Gravel packing is applied by asmulti-layer packs.

[0330] P. Use of Composite Particles in the Sports Field

[0331] Artificial turf has been developed to reduce the expenses ofmaintaining athletic playing areas, and to increase the durability ofthe turf surface, especially where professional sports are involved.

[0332] Artificial turf generally involves a carpet-like pile fabric witha flexible backing laid on a compacted substrate, such as crushed stoneor other stabilized base material. The pile fabric has rows ofupstanding synthetic ribbons representing glass blades extendingupwardly from the top surface of the backing. Of particular interest tothe present invention are the various formulations for granularresilient fill that is placed between the upstanding ribbons on theupper surface of the backing to simulate the presence of soil. Mostprior art systems involve some use of sand or crushed slag particles,together with a resilient foam backing or crumb rubber particles toprovide resilience.

[0333] For example, U.S. Pat. No. 3,995,079 to Haas, Jr., incorporatedherein by reference, discloses a use of a turf pile fabric for coveringa golf green. The infill is a selection from granulated coal slag,crushed flint or crushed granite. A foam resilient underpad providessome resilience, however, the angular particles of the infill arerelatively abrasive. Where abrasion is a problem such as games offootball, rugby, soccer, field hockey, baseball and other games whereplayers may fall down or be knocked down on the playing surface, thereis a need to provide resilient materials which are not abrasive on thegranular infill. For example, U.S. Pat. No. 4,337,283 to Haas, Jr.,incorporated herein by reference, discloses mixing of fine hard sandparticles with 25% to 95% by volume resilient particles to provide animproved resilient and non-abrasive soil imitating infill. Suchresilient material may include mixtures of granulated rubber particles,cork polymer beads, foam rubber particles, vermiculite, and the like.

[0334] U.S. Pat. No. 5,958,527, incorporated herein by reference, alsodiscloses artificial turf employing a pile fabric with a flexible sheetbacking and rows of upstanding synthetic ribbons representing grassblades, extending upwardly from an upper surface of the backing. Aninfill layer of multiple distinct graded courses of particulate materialis disposed interstitially between the upstanding ribbons upon the uppersurface of the backing and at a depth less than the length of theribbons.

[0335] If desired, the composite particles of the present invention maybe employed for use with artificial turf. Such composite particles aremade of filler and a polymer latex synthetic rubber, such as acarboxylated styrene/butadiene copolymer, ethylene propylene dienemonomer (EPDM) rubber, or other elastomer. A typical carboxylatedstyrene/butadiene copolymer is BAYPREN latex, available from Bayer. Thecomposition may further comprise additives such as an emulgator (whichis a non-ionic emulsifier), 1-2 weight % anti-oxidant as an anti-agingagent, and 5 to 10 weight % zinc oxide as a strength enhancer. If tooelastic, a phenol may be added to modify the latex. The mixture offiller, binder and additives is cured by heat to form particles. Theparticles are optionally coated. However, uncoated particles arepreferred.

[0336] These particles may be employed on artificial turf sports fieldsto provide a safe comfortable playing surface. The particles have aresiliency alone or when mixed with sand to provide the same bounce as areal grass field. This is achieved by balancing the composition andamount of the polymer coated on each core, the weight ratio of coatedparticles to uncoated sand, and the depth of the layer of coatedparticles and/or uncoated sand applied to the sports field.

[0337]FIG. 14 shows a first embodiment of a sports field 900 employingthe particles of the present invention. Field 900 comprises a porousrubber mat 902 placed on the ground surface. Blades 904 of artificialgrass extend upwardly from the mat 902 and protrude through a layer 906of latex-filler particles of the present invention. Layer 906 may be100% latex-filler particles of the present invention which generallyfills 10 to 25% of the blade 904 height. Typical composite particleshave a size from about 15 to about 70 USS mesh.

[0338]FIG. 15 shows a second embodiment 909 of a portion of a sportsfield employing the present invention wherein a layer of sand 910 isplaced over the mat 902 and a layer 920 of latex-filler particles of thepresent invention is placed over the layer of sand 910. The combinedheight of layer 910 and layer 920 generally fills 10 to 25% of the blade904 height. Typical sand particle size ranges from about 20 to about 50USS mesh. However, in some instances, such as surfaces for runningracehorses, larger sand particles, e.g., as large as about 15 mesh maybe employed. Typical composite particles have a size from about 15 toabout 70 USS mesh. For example, the weight ratio of the sand tocomposite particles may range from about 5 to about 95:about 95 to about5. A typical weight ratio of sand to composite is about 1 to about3:about 3 to about 1.

[0339] For example, a typical artificial grass sports field of thepresent invention would employ stress relieving composite particles ofthe present invention packed with sand into a sand pack. Such sportsfields are suitable for American football, baseball, European football(Soccer), tennis, golf tee-offs, field hockey, etc.

[0340] The present invention solves a problem, common to currentartificial grass sports fields, of having insufficient “elasticity”built-in into their sand. Insufficient “elasticity” is a cause ofinjuries and undesired bouncing of the game ball.

[0341] One of the many potential advantages of the present invention isto provide fields with more elasticity, yet also having the ability torelieve stress. This contrasts with current artificial grass sportsfields which use particles of shredded tires and, as a result, are tooelastic and difficult to stabilize in the sand pack.

[0342] A typical composite of the present invention for use inartificial grass sports fields comprises filler particles and a binderof polymer latex. The composite particles may be made by anyconventional method for making granules or pellets of latex with fillerparticles. For example, a mixer/granulator, extruder or other suitabledevice may be employed. One suitable binder is PERBUNAN X 1120 fromBASF-Germany which has ±45% solids and a pH of 7.5. This binder is anaqueous, plasticizer-free dispersion of a butadiene-acrylonitrilecopolymer that can be crosslinked by heat. This binder already containsan anionic-nonionic emulsifier and is stabilized with an antioxidant.The heat treatment is generally at temperatures between 120-150° C. andthe reaction is accelerated by catalysts, e.g., ammonium nitrate andmaleic acid or phosphoric acid. After being completely crosslinked,these binders are insoluble in most organic solvents and water. Theymight swell but that is an advantage for use in artificial grass sportsfields. Possibly the binders may be contacted with extra vulcanizationchemicals to improve hardness and strength. It is desirable to employ astrong granulate with partial, yet instant, elasticity under stress andwhich immediately returns to its pre-stressed shape after the stress isgone. Another desirable feature is to make the composite particles ofmaterials which avoid leaching chemicals which might hurt the playersusing the sports field. Another embodiment, not shown, mixes theaforementioned sand and composite particles as a single layer. Forexample, the weight ratio of the sand to composite particles may rangefrom about 5 to about 95:about 95 to about 5. A typical weight ratio ofsand to composite is about 1 to about 3:about 3 to about 1.

EXAMPLES 1-12

[0343] The invention is explained in more detail in the following, withtwelve compositions as example embodiments, and with modifications ofthe above-described processes of FIGS. 1-3. As stated above, theaccompanying drawings show:

[0344]FIG. 1: A first embodiment of a process for making compositeparticles of the present invention.

[0345]FIG. 2: A second embodiment of a process for making compositeparticles of the present invention.

[0346]FIG. 3: A third embodiment of a process for making compositeparticles of the present invention.

[0347] Twelve compositions were made to have the compositions listed inTABLE 3. The volume proportions refer to the finally cured “compositeproppant” while the weights refer to the composition before granulation.The quartz sand (“Q” indicates quartz) have a SiO₂ content >98.3%,fineness of grind, d₅₀=6 μm and density of 2.63 g/cm³. The aluminumoxide (indicated by “A”) has ≧99% Al₂O₃, fineness of grind, d₅₀=7.5 μm,and density of 3.96 g/cm³. A fluid phenol-formaldehyde resole resin(symbolized by “P”) and a viscous resole resin (indicated by “F”) wereused as the synthetic resins, with water as the solvent. Thephenol-formaldehyde resoles, used in this process have a ratio betweenphenol:formaldehyde of 1:1.1 to 1:1.9. Typical ratios are around 1:1.2to 1.5. The fineness of the quartz sand and other fillers also can beused in the range d₅₀=3-45 μm. TABLE 3 Example No. Mineral Syntheticresin Solvent 1  860 g 65% Q v/v 215 g 35% P v/v 20 g 2  927 g 70% Q v/v185 g 30% P v/v 18 g 3  993 g 75% Q v/v 155 g 25% P v/v 15 g 4 1267 g65% A v/v 215 g 35% P v/v 20 g 5 1365 g 70% A v/v 185 g 30% P v/v 18 g 61492 g 75% A v/v 155 g 25% P v/v 15 g

[0348] Use of resole resin F at the same proportions of Examples 1-6gives the compositions of Examples 7-12, respectively.

[0349] These compositions were first compressed at 53 Mpa into test barswith dimensions 5×5×56 mm and put in a dry box at 160 to 240° C. andcured for ten minutes. In view of the ability to granulate, thecompositions with 65% by volume mineral, which generally had the highestbending resistance, were preferred for processing into proppantgranulations with grain sizes from about 0.4 mm to about 0.8 mm, (20/40mesh size) according to the process of FIG. 1.

EXAMPLES 13-18

[0350] Particles dried at 80° C., in accordance with the process of FIG.2, but not cured, were subjected to mechanical refining of the surfaceto smooth it and make it approximate a spherical shape. That was doneeither by putting the granules in a granulating pan with a high tiltangle and high rotational speed, or by processing them in a SPHERONIZERdevice at 400-1000 rpm for 3-30 minutes. The smoothing occurred by aremoval process (grinding process) in which the particles in a profiledrotating pan were thrown out against a cylindrical wall and then rolledback onto the plate.

[0351] According to the process of FIG. 3, the finished cured particleswere formed using about 70% by weight of their final synthetic resincontent and then were surface-coated with the remaining 30% by weight ofthe synthetic resin on a rotating disk.

[0352] The individual particles listed in TABLE 4, serially numbered,were produced and examined to determine their principal parameters, suchas density, sphericity and Brinell hardness:

[0353] Example No. 13, composition of Example 1, made according to theprocess of FIG. 1.

[0354] Example No. 14, composition of Example 1, made according to theprocess of FIG. 2, with later smoothing in a SPHERONIZER device.

[0355] Example No. 15, composition of Example 1, made according to theprocess of FIG. 3, with second curing in a dry box.

[0356] Example No. 16, composition of Example 1, made according to theprocess of FIG. 3, with second curing in a rotary kiln.

[0357] Example No. 17, composition of Example 7, made according to theprocess of FIG. 1. TABLE 4 Example Bulk density Grain density Brinellhardness No. (g/cm³) (g/cm³) Sphericity (Mpa) 13 1.12 1.87 0.82 123.7 141.19 1.98 0.84 102.3 15 1.29 2.15 0.92 151.0 16 1.14 1.90 0.92 129.0 171.12 1.87 >0.8 >100.0

[0358] Of these Examples, Example 15 was found to be particularlypromising for the intended use, and its characteristics were studied inmore detail. The following data of TABLE 5 were found for the effect ofthe curing temperature, with a curing time of 30 minutes, on the bendingstrength of test pieces of Example No. 15. They also allow conclusionsabout other strength characteristics: TABLE 5 Curing FlexuralTemperature Strength 160° C. 89 Mpa 180° C. 72 Mpa 200° C. 81 Mpa 220°C. 80 Mpa 240° C. 72 Mpa 260° C. 26 Mpa 280° C. 22 Mpa 300° C. 22 Mpa

[0359] A crush test according to API RP 56/60, modified as follows, wasalso done on a sample of Example No. 15 cured for 30 minutes at 180° C.:

[0360] a) Fill a crush cell 31 mm in diameter with granulation to aheight of 10 mm.

[0361] b) Increase the compressive load in steps to about 100 Mpa(14,500 psi), recording the deformation of the granulate pack at twotest temperatures, 20° C. and 125° C.

[0362] The results are shown in TABLE 6: TABLE 6 Deformation DeformationPressure Pressure (mm) (mm) (Mpa) (psi) @ 20° C. @ 125° C.  0.29   420.06  0.54   78 0.08  0.60   87 0.10  1.16  168 0.16  1.23  178 0.13 2.90  420 0.27  3.10  449 0.23  5.92  858 0.40  6.29  912 0.34 12.00 1739 0.65 12.60  1826 0.50 24.25  3514 0.95 25.19  3651 0.77 36.57 5300 1.36 37.69  5462 1.03 49.10  7116 1.80 50.15  7268 1.31 61.48 8910 2.21 61.98  8983 1.60 74.33 10772 2.55 75.77 10981 1.90 87.2712648 2.83 88.58 12838 2.18 98.12 14220 3.01 99.30 14391 2.37

[0363] The following values of TABLES 7 and 8 were also determined forthe same sample: TABLE 7 Breaking strength in the composite proppantstackpack  52 Mpa 0.99% by weight breakage  69 Mpa 2.39% by weightbreakage  86 Mpa 4.18% by weight breakage 103 Mpa 7.10% by weightbreakage

[0364] TABLE 8 Particle size distribution Screen mesh Retained, %Cumulative, width in mm by weight % by weight 1.0 0.0 100.00 0.8 1.3298.68 0.71 4.62 94.06 0.63 15.47 78.59 0.50 48.15 30.44 0.40 27.06 3.380.25 3.88 0.00 <0.25 0.0 —

[0365] The acid solubility of this Example No. 15, by API RP 56/60, was4.4% by weight.

EXAMPLES 18-20

[0366] TABLES 9 and 10 show recommended parameter values and actualparameters of Examples 19-21 made by a process of FIG. 3. TABLE 9 Recom-Property mended Example Example Example Measured Limits 18 19 20 APIMesh 20/40 20/40 20/40 20/40 Size Nominal Resin — 14.6 16.7 15.5Content, loss on ignition (LOI), weight % Curable — 0.2 0.4 — ResinContent, % of LOI Particle Size weight % retained Distribution U.S.Example Example Standard 19A 19B Sieve No. “as is” “re- (mm) sieved”U.S. Example Example Standard 19A 19B Sieve No. “as is” “re- (mm)sieved”   16 (1.19) <0.1 0.0 0.0 0.0 —   18 (1.00) — — — — 0.0   20(0.84) — 0.0 0.0 0.0 — −23 (0.80) — — — — 1.3   25 (0.71) — 13.5 1.3 1.54.6 −28 (0.63) — — — — 15.5   30 (0.589) — 41.0 16.7 18.7 —   35 (0.50)— 26.0 29.4 33.0 48.2   40 (0.42) — 14.6 41.8 46.8 — −42 (0.40) — — — —27.0   50 (0.297) — 4.8 10.7 0.0 —   60 (0.25) — — — — 3.4 pan <1.0 0.10.1 0.0 0.0 (<0.297 or <0.25) TOTAL 100.0 ± 100.0 100.0 100.0 100.0 0.5in-size, ≧90.0 95.1 89.2 100.0 95.3 −20+40 mesh, (0.84- 0.42 mm) mean —0.023 0.020 0.021 — particle (0.59) (0.50) (0.52) diameter, inch (mm)Turbidity, ≦500 60 80 — — NTU (FTU)

[0367] TABLE 9 Recommended Example Example Example Property MeasuredLimits 18 19 20 Crush Resistance weight % fines generated @ ClosureStress, psi (Mpa) 15,000 (103) ≦10 5.4 12.8 7.1 12,500 (86) 3.4 8.5 4.210,000 (69) 1.9 5.5 2.4  7,500 (52) 0.9 3.6 1.0  6,000 (41) — 2.6 — 5,000 (36) — 2.2 —  4,000 (28) ≦4 — 2.0 —  3,000 (21) — 1.8 —  2,000(14) — 1.6 — Krumbein Shape Factors roundness ≧0.9 0.8 0.7 0.9sphericity ≧0.9 0.8 0.8 0.8 Acid Solubility, ≦1.0 4.4 0.27 <1 weight %Clusters weight % ≦1.0 1.1 1.5 5 Density, Bulk, ≦1.3 1.29 1.21 1.22g/cm³ (lb_(m)/ft³) (81) (80.5) (75.5) (76.2) Density, Absolute ≦about2.22 2.13 2.10 (particle) 2.20 (18.5) (17.8) (17.5) g/cm³ (lb_(m)/gal)(18.4) weight % fines generated Crush Resistance** 5.5 — 6.2 @ ClosureStress 10,000 psi (69 Mpa)

[0368] TABLE 11 shows conductivity and permeability data. TABLE 12 liststest procedures for properties listed for proppant of various examples.TABLE 11 Short-term Conductivity & Permeability of Example 20 Proppants200° F. (93° C.) Example 19A Example 19B deionized water sample “as is”excluding >40 particles between stainless steel shims Closure Stress,psi (Mpa) Conductivity, md-ft (Permeability, darcy) 2,000 (14) 3251(143) 4209 (181) 4,000 (28) 1080 (53)  960 (47) 6,000 (41) 216 (11) 253(13) 8,000 (56) 80 (4) 88 (5)

[0369] TABLE 12 Property Measured Procedure Acid Solubility API RP-56,section 6 Density, Absolute (Particle) API RP-60, section 8 Density,Bulk API RP-60, section 8 Clusters (agglomeration) API RP-56, section5.5 Crush Resistance API RP-56/60, section 8/7 Particle SizeDistribution API RP-56/60, section 4, Short-term Conductivity API RP-61Turbidity API RP-56, section 7, Method 1, modified

[0370] While specific embodiments of the composition and method aspectsof the invention have been shown and described, it should be apparentthat many modifications can be made thereto without departing from thespirit and scope of the invention. Accordingly, the invention is notlimited by the foregoing description, but is only limited by the scopeof the claims appended thereto.

What is claimed is:
 1. A composite particle comprising: a substantiallyhomogeneous formed particle comprising: a first portion of a binder,wherein the first portion is at least partly cured; filler particlesdispersed throughout the first portion of binder, wherein particle sizeof the filler particles ranges from about 0.5 to about 60 μm; and anoptional second portion of a binder coating the formed particle; whereinthe first and second portions of binder have an absence of cement;wherein at least one member of the group consisting of the first portionof binder or the second portion of binder comprises a cold-set resin,wherein the composite particle has a bulk density of 0.50 to 1.30 gramsper cubic centimeter.
 2. The composite particle of claim 1, wherein thecomposite particle bulk density ranges from about 50 to about 80.5lbs/ft³.
 3. The composite particle of claim 1, wherein 60 to 85 volumepercent of the composite particle is the filler particles.
 4. Thecomposite particle of claim 1, wherein 60 to 80 volume percent of thecomposite particle is the filler particles.
 5. The composite particle ofclaim 1, wherein 60 to 75 volume percent of the composite particle isthe filler particles.
 6. The composite particle of claim 1, wherein thecomposite particle has a sphericity of at least about 0.7.
 7. Thecomposite particle of claim 1, wherein the composite particle has agrain density of 0.90 to 2.20 gm/cm³.
 8. The composite particle of claim1, wherein the composite particle has a grain density of 1.40 to 1.60gm/cm³.
 9. The composite particle of claim 1, wherein the fillercomprises at least one member selected from the group consisting offinely divided minerals, fibers, ground almond shells, ground walnutshells, and ground coconut shells.
 10. The composite particle of claim1, wherein the filler particles comprise at least one member selectedfrom the group consisting of fly ash, hollow glass microspheres, groundalmond shells, ground coconut shells and ground walnut shells.
 11. Thecomposite particle of claim 1, wherein at least one member of the groupconsisting of the first portion of binder or the second portion ofbinder comprises at least one member of the group consisting of novolacresin, resole resin, and further comprises cross-linking agents andconventional additives.
 12. The composite particle of claim 1, whereinat least one member of the group consisting of the first portion ofbinder or the second portion of binder comprises at least one member ofthe group consisting of epoxy resin, polyurethane resin, alkalinemodified phenolic resole curable with ester, melamine resin,urea-aldehyde resin, urea-phenol-aldehyde resin, furans, syntheticrubber, polyester resin, and further comprises cross-linking agents andconventional additives.
 13. The composite binder of claim 1, whereineach portion of binder comprises at least one polymerized monomer oroligomer selected from the group consisting of melamine, urea,formaldehyde, phenol, bisphenol, isocyanate, epoxy resin,epichlorohydrin, and furfuryl alcohol.
 14. The composite particle ofclaim 1, wherein at least one said portion of the binder comprisesinorganic binder or alkoxy modified resole resin.
 15. The compositeparticle of claim 1, wherein the composite particles have diameters from4 to 100 mesh.
 16. The composite particle according to claim 1, whereinthe composite particles have diameters between 20 and 40 mesh andcomprise a coating of a layer of synthetic resin.
 17. The compositeparticle according to claim 1, wherein the composite particles havediameters between 30 and 40 mesh and comprise a coating of a layer ofsynthetic resin.
 18. The composite particle according to claim 1,wherein the composite particles have diameters between 8 and 20 mesh andcomprise a coating of a layer of synthetic resin.
 19. The compositeparticle of claim 1, wherein the first portion of binder comprises acured binder, and the second portion of binder comprises a curablebinder.
 20. The composite particle of claim 1, wherein the fillerparticles have a grain size, d₅₀, of 4 to 10 μm.
 21. The compositeparticle of claim 1, wherein the filler particles are about 45 to 80% byweight of the composite particle.
 22. The composite particle of claim 1,wherein the filler particles are about 60 to 75% by weight of thecomposite particle.
 23. The composite particle of claim 1, wherein thefiller particles are about 70 to 80% by weight of the compositeparticle.
 24. A method for producing a composite particle according toclaim 1, comprising mixing the filler particles, the first portion ofbinder, at least one member of the group consisting of water and anorganic solvent, and optional additives to form a mixture and to adjustagglomeration behavior of the filler particles; subjecting the mixtureto agglomerative granulation to form cores; and curing the first portionof binder.
 25. The method according to claim 24, wherein the curing ofthe first and second portions of binder is a cold set curing.
 26. Themethod according to claim 24, further comprising coating the cores withsaid second portion of binder and curing said coating by a cold setcuring.
 27. The method according to claim 25, wherein the agglomerativegranulating is done by extrusion as strands, cutting the strands intofragments, and shaping the fragments under the influence of centrifugalforce into spherical granules.
 28. The method according to claim 25,wherein the formed particles are smoothed and compressed by rollingbefore crosslinking of the binder.
 29. The method according to claim 25,wherein after the first portion of binder has cured, the formedparticles are coated with the second portion of binder and cured again.30. The method according to claim 25, wherein after granulation thesolvent is dried, and after the drying but, before curing the firstportion of binder, the formed particles are coated with resin.
 31. Amethod of treating a hydraulically induced fracture in a subterraneanformation surrounding a wellbore comprising introducing a proppantcomprising composite particles of claim 1 into the fracture.
 32. Themethod according to claim 31, wherein a multi-layer pack comprising thecomposite particles is formed in the formation.
 33. The method accordingto claim 31, wherein the first portion of binder comprises a resoleresin and the second portion of binder comprises a polyurethane resin oran alkaline modified resole curable with ester.
 34. The method of claim31, wherein the proppant further comprises particles selected from atleast one member of the group consisting of sand, sintered ceramicparticles and glass beads.
 35. The method of claim 31, wherein thefiller particles have a grain size, d₅₀, of 4 to 10 μm.
 36. A method forwater filtration comprising passing water through a filtration packcomprising the composite particles of claim
 1. 37. A method for forminga gravel pack about a wellbore comprising introducing the compositeparticles of claim 1 and gravel into the well bore.
 38. An artificialturf sports field, comprising a porous mat and a layer comprising theparticles of claim 1 over the mat, wherein the first and optional secondportions of binder comprise an elastomer.
 39. An artificial turf sportsfield, comprising a porous mat and a layer of the particles of claim 1over the mat, wherein the binder comprises an elastomer.
 40. A methodfor preparing an artificial turf sports field comprising providing aporous mat and applying a layer comprising the composite particles ofclaim 1 over the mat, wherein the first portion of binder comprises anelastomer.
 41. The method for preparing an artificial turf sports fieldof claim 40, wherein the second portion of binder comprises anelastomer.
 42. The method for preparing an artificial turf sports fieldof claim 40, wherein a mixture of sand and the composite particles isapplied to the mat to form the layer.
 43. The method for preparing anartificial turf sports field of claim 40, wherein only the compositeparticles are applied to the mat to form the layer.
 44. A compositeparticle comprising: a substantially homogeneous formed particlecomprising: a core comprising a binder and filler particles dispersedthroughout the binder, wherein particle size of the filler particlesranges from about 0.5 to about 60 μm; wherein the composite particle hasa bulk density of 0.50 to 1.30 grams per cubic centimeter, and a graindensity of 0.90 to about 2.2 gr/cm³; optionally the particle has a resincoating.
 45. The composite particle of claim 44, wherein the resincoating comprises a cold-set resin.
 46. The composite particle accordingto claim 44, wherein the binder comprises a cement/phenolic polymercomposition, a cement/polyamide composition or a cement/polyimidecomposition.
 47. The composite particle according to claim 44, whereinthe binder comprises an MDF cement.
 48. The composite particle accordingto claim 44, wherein the binder comprises a cement and a polymer. 49.The composite particle according to claim 44, wherein the bindercomprises a cement and a polymer, and the filler particles compriseparticles having a grain density of 2.45 to 3.20 gr/cm³ and particlesselected from at least one member of the group consisting of glassmicrospheres, fly ash, ground almond shells, ground coconut shells, andground walnut shells.
 50. A method for producing a composite particleaccording to claim 44, comprising mixing the filler particles, the firstportion of binder, at least one member of the group consisting of waterand an organic solvent, and optional additives to form a mixture and toadjust agglomeration behavior of the filler particles; subjecting themixture to agglomerative granulation to form cores; and curing the firstportion of binder.
 51. A method of treating a hydraulically inducedfracture in a subterranean formation surrounding a wellbore comprisingintroducing composite particles of claim 44 into the fracture.
 52. Amethod for water filtration comprising passing water through afiltration pack comprising the composite particles of claim
 44. 53. Amethod for forming a gravel pack about a wellbore comprising introducingthe composite particles of claim 44 and gravel into the well bore.